first commit of refactor

2026-02-27 09:58:18 -05:00
commit 0adfd70853
63 changed files with 10558 additions and 0 deletions
--- a/README.md
+++ b/README.md
@@ -0,0 +1,95 @@
+# Koin Ping
+
+A lightweight on-chain monitoring and alerting system designed to give users situational awareness over blockchain addresses they care about.
+
+## Overview
+
+Koin Ping is designed to reliably observe on-chain activity and notify users when predefined conditions are met. It does not execute transactions, manage wallets, or speculate on prices.
+
+## Project Structure
+
+```
+koin_ping/
+├── backend/                  # Node.js + Express + PostgreSQL backend
+│   ├── api/                 # API endpoints and server configuration
+│   ├── poller/              # Blockchain polling logic
+│   ├── alerts/              # Alert evaluation and management
+│   ├── notifications/       # Notification delivery system
+│   ├── domain/              # Domain models and business logic
+│   ├── infra/               # Infrastructure (database, external services)
+│   └── shared/              # Shared utilities and helpers
+│
+└── frontend/                 # React + Vite frontend
+    ├── public/              # Static assets
+    └── src/
+        ├── api/             # Frontend API calls to backend
+        ├── components/      # Reusable UI components
+        ├── pages/           # Top-level pages (views)
+        └── utils/           # Utility functions
+
+```
+
+## Tech Stack
+
+### Backend
+- **Runtime:** Node.js
+- **Framework:** Express
+- **Database:** PostgreSQL
+- **Key Dependencies:** 
+  - `pg` - PostgreSQL client
+  - `dotenv` - Environment variable management
+  - `cors` - CORS middleware
+  - `nodemon` - Development auto-reload
+
+### Frontend
+- **Framework:** React 19
+- **Build Tool:** Vite
+- **Language:** JavaScript/TypeScript (mixed)
+- **Type Checking:** TypeScript
+
+## Getting Started
+
+### Prerequisites
+- Node.js (v18 or higher recommended)
+- PostgreSQL database
+- npm or yarn
+
+### Backend Setup
+
+1. Navigate to the backend directory:
+   ```bash
+   cd backend
+   ```
+
+2. Install dependencies (already done):
+   ```bash
+   npm install
+   ```
+
+3. Create a `.env` file (see backend/README.md for required variables)
+
+4. Start the development server:
+   ```bash
+   npm run dev
+   ```
+
+The backend will run on `http://localhost:3001`
+
+### Frontend Setup
+
+1. Navigate to the frontend directory:
+   ```bash
+   cd frontend
+   ```
+
+2. Install dependencies (already done):
+   ```bash
+   npm install
+   ```
+
+3. Start the development server:
+   ```bash
+   npm run dev
+   ```
+
+The frontend will run on `http://localhost:3000`
--- a/backend/.gitignore
+++ b/backend/.gitignore
@@ -0,0 +1,7 @@
+node_modules/
+.env
+*.log
+.DS_Store
+dist/
+build/
+
--- a/backend/ENV_TEMPLATE.md
+++ b/backend/ENV_TEMPLATE.md
@@ -0,0 +1,51 @@
+# Environment Variables Template
+
+Copy this to `.env` in the backend directory and fill in your values.
+
+```bash
+# Server Configuration
+PORT=3001
+NODE_ENV=development
+
+# Database Configuration
+DATABASE_URL=postgresql://user:password@localhost:5432/koin_ping
+
+# Ethereum JSON-RPC Endpoint
+# Examples:
+#   - Infura: https://mainnet.infura.io/v3/YOUR-PROJECT-ID
+#   - Alchemy: https://eth-mainnet.g.alchemy.com/v2/YOUR-API-KEY
+#   - Local node: http://localhost:8545
+ETH_RPC_URL=https://mainnet.infura.io/v3/YOUR-PROJECT-ID
+
+# Polling interval in milliseconds
+# Default: 60000 (1 minute)
+POLL_INTERVAL_MS=60000
+
+# Firebase Configuration (for authentication)
+# Get this from Firebase Console > Project Settings > Project ID
+FIREBASE_PROJECT_ID=koin-ping
+```
+
+## Quick Setup
+
+```bash
+cd backend
+cp ENV_TEMPLATE.md .env
+# Edit .env with your actual values
+```
+
+## Firebase Setup
+
+For Firebase Admin SDK to work, you need to set up Application Default Credentials:
+
+**Option 1: Use Firebase Project ID (easiest for development)**
+- Just set `FIREBASE_PROJECT_ID` in .env
+- Firebase Admin will use Application Default Credentials
+
+**Option 2: Use Service Account Key (production)**
+1. Go to Firebase Console > Project Settings > Service Accounts
+2. Click "Generate new private key"
+3. Download the JSON file
+4. Either:
+   - Set `GOOGLE_APPLICATION_CREDENTIALS=/path/to/serviceAccountKey.json` in .env
+   - Or keep it in backend/ and add to .gitignore
--- a/backend/README.md
+++ b/backend/README.md
@@ -0,0 +1,56 @@
+# Koin Ping Backend
+
+On-chain monitoring and alerting system backend.
+
+## Environment Variables
+
+Create a `.env` file in the backend directory with the following variables:
+
+```env
+PORT=3001
+NODE_ENV=development
+
+# PostgreSQL Database Configuration
+DB_HOST=localhost
+DB_PORT=5432
+DB_USER=your_db_user
+DB_PASSWORD=your_db_password
+DB_NAME=koin_ping
+
+# Blockchain RPC Endpoints (examples)
+ETH_RPC_URL=https://mainnet.infura.io/v3/YOUR_INFURA_KEY
+POLYGON_RPC_URL=https://polygon-rpc.com
+
+# Polling Configuration
+POLL_INTERVAL_MS=10000
+```
+
+## Getting Started
+
+1. Install dependencies:
+   ```bash
+   npm install
+   ```
+
+2. Set up your `.env` file with the required environment variables
+
+3. Run the development server:
+   ```bash
+   npm run dev
+   ```
+
+4. Run in production:
+   ```bash
+   npm start
+   ```
+
+## Project Structure
+
+- `api/` - API endpoints and server configuration
+- `poller/` - Blockchain polling logic
+- `alerts/` - Alert evaluation and management
+- `notifications/` - Notification delivery system
+- `domain/` - Domain models and business logic
+- `infra/` - Infrastructure (database, external services)
+- `shared/` - Shared utilities and helpers
+
--- a/backend/api/routes/addresses.js
+++ b/backend/api/routes/addresses.js
@@ -0,0 +1,20 @@
+import express from 'express';
+import { authenticate } from '../../middleware/authenticate.js';
+import * as AddressController from '../../controllers/AddressController.js';
+
+const router = express.Router();
+
+// Apply authentication to all routes
+router.use(authenticate);
+
+// POST /addresses - Create Blockchain Address
+router.post('/', AddressController.create);
+
+// GET /addresses - List Addresses
+router.get('/', AddressController.list);
+
+// DELETE /addresses/:addressId - Delete Address
+router.delete('/:addressId', AddressController.remove);
+
+export default router;
+
--- a/backend/api/routes/alertEvents.js
+++ b/backend/api/routes/alertEvents.js
@@ -0,0 +1,12 @@
+import express from 'express';
+import { authenticate } from '../../middleware/authenticate.js';
+import * as AlertEventController from '../../controllers/AlertEventController.js';
+
+const router = express.Router();
+
+router.use(authenticate);
+
+router.get('/', AlertEventController.list);
+
+export default router;
+
--- a/backend/api/routes/alerts.js
+++ b/backend/api/routes/alerts.js
@@ -0,0 +1,18 @@
+import express from 'express';
+import { authenticate } from '../../middleware/authenticate.js';
+import * as AlertRuleController from '../../controllers/AlertRuleController.js';
+
+const router = express.Router();
+
+router.use(authenticate);
+
+router.post('/:addressId/alerts', AlertRuleController.create);
+
+router.get('/:addressId/alerts', AlertRuleController.listByAddress);
+
+router.patch('/:alertId', AlertRuleController.updateStatus);
+
+router.delete('/:alertId', AlertRuleController.remove);
+
+export default router;
+
--- a/backend/api/routes/notificationConfig.js
+++ b/backend/api/routes/notificationConfig.js
@@ -0,0 +1,16 @@
+import express from 'express';
+import { authenticate } from '../../middleware/authenticate.js';
+import * as NotificationConfigController from '../../controllers/NotificationConfigController.js';
+
+const router = express.Router();
+
+router.use(authenticate);
+
+router.get('/', NotificationConfigController.getConfig);
+
+router.put('/', NotificationConfigController.updateConfig);
+
+router.delete('/', NotificationConfigController.deleteConfig);
+
+export default router;
+
--- a/backend/api/routes/status.js
+++ b/backend/api/routes/status.js
@@ -0,0 +1,17 @@
+import express from 'express';
+
+const router = express.Router();
+
+// GET /status - System Status (mock)
+router.get('/', (req, res) => {
+  // TEMP - Mock response until poller service is complete
+  res.json({
+    latestBlock: 0,
+    lag: 0,
+    status: 'healthy',
+    timestamp: new Date().toISOString()
+  });
+});
+
+export default router;
+
--- a/backend/api/server.js
+++ b/backend/api/server.js
@@ -0,0 +1,47 @@
+import express from 'express';
+import cors from 'cors';
+import dotenv from 'dotenv';
+import addressesRouter from './routes/addresses.js';
+import alertsRouter from './routes/alerts.js';
+import alertEventsRouter from './routes/alertEvents.js';
+import statusRouter from './routes/status.js';
+import notificationConfigRouter from './routes/notificationConfig.js';
+
+dotenv.config();
+
+const app = express();
+const PORT = process.env.PORT || 3001;
+
+app.use(cors());
+app.use(express.json());
+
+// Health check
+app.get('/api/health', (req, res) => {
+  res.json({ 
+    status: 'ok', 
+    timestamp: new Date().toISOString(),
+    service: 'koin-ping-backend'
+  });
+});
+
+
+app.use('/api/addresses', addressesRouter);
+app.use('/api/addresses', alertsRouter); // Alert routes include addressId in path
+app.use('/api/alerts', alertsRouter); // Direct alert operations (PATCH, DELETE)
+app.use('/api/alert-events', alertEventsRouter);
+app.use('/api/status', statusRouter);
+app.use('/api/notification-config', notificationConfigRouter);
+
+app.use((err, req, res, next) => {
+  console.error(err.stack);
+  res.status(500).json({ 
+    error: 'Something went wrong!',
+    message: process.env.NODE_ENV === 'development' ? err.message : undefined
+  });
+});
+
+app.listen(PORT, () => {
+  console.log(`Server running on port ${PORT}`);
+  console.log(`Environment: ${process.env.NODE_ENV || 'development'}`);
+});
+
--- a/backend/controllers/AddressController.js
+++ b/backend/controllers/AddressController.js
@@ -0,0 +1,82 @@
+import * as AddressModel from '../models/AddressModel.js';
+
+/**
+ * Create a new address
+ */
+export async function create(req, res) {
+  const { address, label } = req.body;
+  const user_id = req.user_id; // From authenticate middleware
+
+  console.log(`User ${user_id} creating address: ${address}`);
+
+  if (!address) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Address is required'
+    });
+  }
+
+  // Validation:  ETH address format
+  if (!/^0x[a-fA-F0-9]{40}$/.test(address)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid Ethereum address format'
+    });
+  }
+
+  try {
+    const newAddress = await AddressModel.create(user_id, address, label || null);
+    console.log(`Address created with ID: ${newAddress.id}`);
+    return res.status(201).json(newAddress);
+  } catch (error) {
+    // Handle duplicate address (unique constraint violation)
+    if (error.code === '23505') {
+      return res.status(400).json({
+        error: 'VALIDATION_ERROR',
+        message: 'You are already tracking this address'
+      });
+    }
+    throw error;
+  }
+}
+
+
+export async function list(req, res) {
+  const user_id = req.user_id; // From authenticate middleware
+  
+  console.log(`User ${user_id} listing addresses`);
+  
+  const addresses = await AddressModel.listByUser(user_id);
+  
+  console.log(`Found ${addresses.length} addresses for user`);
+  
+  return res.json(addresses);
+}
+
+export async function remove(req, res) {
+  const addressId = parseInt(req.params.addressId);
+  const user_id = req.user_id; // From authenticate middleware
+
+  console.log(`User ${user_id} deleting address ID: ${addressId}`);
+
+  if (isNaN(addressId)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid address ID'
+    });
+  }
+
+  const deleted = await AddressModel.remove(addressId, user_id);
+
+  if (!deleted) {
+    console.log(`Address ${addressId} not found or not owned by user`);
+    return res.status(404).json({
+      error: 'NOT_FOUND',
+      message: 'Address not found'
+    });
+  }
+
+  console.log(`Address ${addressId} deleted`);
+  return res.status(204).send();
+}
+
--- a/backend/controllers/AlertEventController.js
+++ b/backend/controllers/AlertEventController.js
@@ -0,0 +1,54 @@
+import * as AlertEventModel from '../models/AlertEventModel.js';
+
+// Mock data for when DB is empty (MVP scaffolding)
+const MOCK_EVENTS = [
+  {
+    id: 1,
+    alert_rule_id: 1,
+    message: 'Incoming transaction detected: 5.5 ETH received',
+    address_label: 'Treasury Wallet',
+    timestamp: new Date(Date.now() - 2 * 60 * 60 * 1000).toISOString() // 2 hours ago
+  },
+  {
+    id: 2,
+    alert_rule_id: 2,
+    message: 'Balance dropped below threshold: Current balance 8.2 ETH',
+    address_label: 'Treasury Wallet',
+    timestamp: new Date(Date.now() - 5 * 60 * 60 * 1000).toISOString() // 5 hours ago
+  },
+  {
+    id: 3,
+    alert_rule_id: 3,
+    message: 'Outgoing transaction detected: 2.0 ETH sent',
+    address_label: 'Cold Storage',
+    timestamp: new Date(Date.now() - 24 * 60 * 60 * 1000).toISOString() // 1 day ago
+  }
+];
+
+
+export async function list(req, res) {
+  const limit = parseInt(req.query.limit) || 20;
+  const user_id = req.user_id; // From authenticate middleware
+
+  console.log(`User ${user_id} listing alert events (limit: ${limit})`);
+
+
+  if (limit < 1 || limit > 100) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Limit must be between 1 and 100'
+    });
+  }
+
+  const events = await AlertEventModel.listRecentByUser(user_id, limit);
+
+  console.log(`Found ${events.length} alert events for user`);
+
+  // Return mock data if DB is empty (MVP scaffolding)
+  if (events.length === 0) {
+    return res.json(MOCK_EVENTS.slice(0, limit));
+  }
+
+  return res.json(events);
+}
+
--- a/backend/controllers/AlertRuleController.js
+++ b/backend/controllers/AlertRuleController.js
@@ -0,0 +1,185 @@
+import * as AlertRuleModel from '../models/AlertRuleModel.js';
+import * as AddressModel from '../models/AddressModel.js';
+
+const VALID_ALERT_TYPES = ['incoming_tx', 'outgoing_tx', 'large_transfer', 'balance_below'];
+const THRESHOLD_REQUIRED_TYPES = ['large_transfer', 'balance_below'];
+
+/**
+ * Create a new alert rule
+ */
+export async function create(req, res) {
+  const addressId = parseInt(req.params.addressId);
+  const { type, threshold } = req.body;
+  const user_id = req.user_id; // From authenticate middleware
+
+  console.log(`User ${user_id} creating alert for address ID: ${addressId}`);
+
+  if (isNaN(addressId)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid address ID'
+    });
+  }
+
+
+  if (!type) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Alert type is required'
+    });
+  }
+
+  // Validation: type must be valid
+  if (!VALID_ALERT_TYPES.includes(type)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: `Invalid alert type. Must be one of: ${VALID_ALERT_TYPES.join(', ')}`
+    });
+  }
+
+
+  if (THRESHOLD_REQUIRED_TYPES.includes(type)) {
+    if (!threshold || threshold === '') {
+      return res.status(400).json({
+        error: 'VALIDATION_ERROR',
+        message: `Alert type '${type}' requires a threshold value`
+      });
+    }
+
+
+    const thresholdNum = parseFloat(threshold);
+    if (isNaN(thresholdNum) || thresholdNum <= 0) {
+      return res.status(400).json({
+        error: 'VALIDATION_ERROR',
+        message: 'Threshold must be a positive number'
+      });
+    }
+  }
+
+  try {
+    // Verify address exists AND belongs to this user
+    const address = await AddressModel.findById(addressId, user_id);
+    if (!address) {
+      console.log(`Address ${addressId} not found or not owned by user`);
+      return res.status(404).json({
+        error: 'NOT_FOUND',
+        message: 'Address not found'
+      });
+    }
+
+    const newAlert = await AlertRuleModel.create(
+      addressId,
+      type,
+      threshold || null
+    );
+
+    console.log(`Alert rule created with ID: ${newAlert.id}`);
+    return res.status(201).json(newAlert);
+  } catch (error) {
+    console.error(error);
+    return res.status(500).json({
+      error: 'INTERNAL_ERROR',
+      message: 'Failed to create alert rule'
+    });
+  }
+}
+
+
+export async function listByAddress(req, res) {
+  const addressId = parseInt(req.params.addressId);
+  const user_id = req.user_id; // From authenticate middleware
+
+  console.log(`User ${user_id} listing alerts for address ID: ${addressId}`);
+
+  if (isNaN(addressId)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid address ID'
+    });
+  }
+
+
+  const address = await AddressModel.findById(addressId, user_id);
+  if (!address) {
+    console.log(`Address ${addressId} not found or not owned by user`);
+    return res.status(404).json({
+      error: 'NOT_FOUND',
+      message: 'Address not found'
+    });
+  }
+
+  const alerts = await AlertRuleModel.listByAddress(addressId);
+  console.log(`Found ${alerts.length} alert rules`);
+  return res.json(alerts);
+}
+
+
+export async function updateStatus(req, res) {
+  const alertId = parseInt(req.params.alertId);
+  const { enabled } = req.body;
+  const user_id = req.user_id; 
+
+  console.log(`User ${user_id} updating alert ID: ${alertId}`);
+
+  // Validation: alertId must be valid
+  if (isNaN(alertId)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid alert ID'
+    });
+  }
+
+  // Validation: enabled must be boolean
+  if (typeof enabled !== 'boolean') {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'enabled must be a boolean value'
+    });
+  }
+
+  // Verify user owns this alert (through address ownership)
+  const alert = await AlertRuleModel.findById(alertId, user_id);
+  if (!alert) {
+    console.log(`Alert ${alertId} not found or not owned by user`);
+    return res.status(404).json({
+      error: 'NOT_FOUND',
+      message: 'Alert rule not found'
+    });
+  }
+
+  const updatedAlert = await AlertRuleModel.updateEnabled(alertId, enabled);
+
+  console.log(`Alert ${alertId} updated: enabled=${enabled}`);
+  return res.json(updatedAlert);
+}
+
+
+export async function remove(req, res) {
+  const alertId = parseInt(req.params.alertId);
+  const user_id = req.user_id; 
+
+  console.log(`User ${user_id} deleting alert ID: ${alertId}`);
+
+  if (isNaN(alertId)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid alert ID'
+    });
+  }
+
+
+  const alert = await AlertRuleModel.findById(alertId, user_id);
+  if (!alert) {
+    console.log(`Alert ${alertId} not found or not owned by user`);
+    return res.status(404).json({
+      error: 'NOT_FOUND',
+      message: 'Alert rule not found'
+    });
+  }
+
+  const deleted = await AlertRuleModel.remove(alertId);
+
+  console.log(`Alert ${alertId} deleted`);
+  return res.status(204).send();
+}
+
--- a/backend/controllers/NotificationConfigController.js
+++ b/backend/controllers/NotificationConfigController.js
@@ -0,0 +1,105 @@
+import * as NotificationConfigModel from '../models/NotificationConfigModel.js';
+
+/**
+ * Get notification config for the authenticated user
+ */
+export async function getConfig(req, res) {
+  const user_id = req.user_id; // From authenticate middleware
+  
+  console.log(`User ${user_id} getting notification config`);
+  
+  const config = await NotificationConfigModel.getConfig(user_id);
+  
+  if (!config) {
+    // Return empty config if not set
+    return res.json({
+      user_id,
+      discord_webhook_url: null,
+      telegram_chat_id: null,
+      email: null,
+      notification_enabled: true
+    });
+  }
+  
+  console.log(`Config found`);
+  return res.json(config);
+}
+
+/**
+ * Update notification config for the authenticated user
+ */
+export async function updateConfig(req, res) {
+  const user_id = req.user_id; // From authenticate middleware
+  const { discord_webhook_url, telegram_chat_id, email, notification_enabled } = req.body;
+  
+  console.log(`User ${user_id} updating notification config`);
+  
+  // Validation: at least one field should be provided
+  if (
+    discord_webhook_url === undefined &&
+    telegram_chat_id === undefined &&
+    email === undefined &&
+    notification_enabled === undefined
+  ) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'At least one configuration field must be provided'
+    });
+  }
+  
+  // Validation: Discord webhook URL format (basic check)
+  if (discord_webhook_url && !discord_webhook_url.startsWith('https://discord.com/api/webhooks/')) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid Discord webhook URL format'
+    });
+  }
+  
+  // Validation: Email format (basic check)
+  if (email && !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email)) {
+    return res.status(400).json({
+      error: 'VALIDATION_ERROR',
+      message: 'Invalid email address format'
+    });
+  }
+  
+  try {
+    const updatedConfig = await NotificationConfigModel.upsertConfig(user_id, {
+      discord_webhook_url,
+      telegram_chat_id,
+      email,
+      notification_enabled
+    });
+    
+    console.log(`Notification config updated`);
+    return res.json(updatedConfig);
+  } catch (error) {
+    console.error('Error updating notification config:', error);
+    return res.status(500).json({
+      error: 'INTERNAL_ERROR',
+      message: 'Failed to update notification configuration'
+    });
+  }
+}
+
+/**
+ * Delete notification config for the authenticated user
+ */
+export async function deleteConfig(req, res) {
+  const user_id = req.user_id; // From authenticate middleware
+  
+  console.log(`User ${user_id} deleting notification config`);
+  
+  const deleted = await NotificationConfigModel.remove(user_id);
+  
+  if (!deleted) {
+    return res.status(404).json({
+      error: 'NOT_FOUND',
+      message: 'No notification configuration found'
+    });
+  }
+  
+  console.log(`Notification config deleted`);
+  return res.status(204).send();
+}
+
--- a/backend/domain/NormalizedTx.js
+++ b/backend/domain/NormalizedTx.js
@@ -0,0 +1,19 @@
+/**
+ * NormalizedTx - Standardized transaction representation
+ * 
+ * Defines the minimal, normalized transaction data relevant
+ * for tracking blockchain activity. 
+ */
+
+/**
+ * @typedef {Object} NormalizedTx
+ * @property {string} hash - Transaction hash (0x prefixed)
+ * @property {string} from - Sender address (lowercase, 0x prefixed)
+ * @property {string|null} to - Recipient address (lowercase, 0x prefixed, null for contract creation)
+ * @property {string} value - Value transferred in Wei (as string to preserve precision)
+ * @property {number} blockNumber - Block number where transaction was included
+ * @property {number} blockTimestamp - Unix timestamp of the block
+ */
+
+export default {};
+
--- a/backend/domain/ObservedTx.js
+++ b/backend/domain/ObservedTx.js
@@ -0,0 +1,17 @@
+
+/**
+ * @typedef {import('./NormalizedTx.js').NormalizedTx} NormalizedTx
+ */
+
+/**
+ * @typedef {Object} ObservedTxMetadata
+ * @property {number} addressId - ID of the tracked address (from addresses table)
+ * @property {'incoming'|'outgoing'} direction - Direction relative to tracked address
+ */
+
+/**
+ * @typedef {NormalizedTx & ObservedTxMetadata} ObservedTx
+ */
+
+export default {};
+
--- a/backend/firebase/admin.js
+++ b/backend/firebase/admin.js
@@ -0,0 +1,20 @@
+
+
+import admin from 'firebase-admin';
+import dotenv from 'dotenv';
+
+dotenv.config();
+
+
+if (!admin.apps.length) {
+  admin.initializeApp({
+    projectId: process.env.FIREBASE_PROJECT_ID,
+    // For local development, you can use application default credentials
+    // or provide a service account key file
+  });
+}
+
+export const auth = admin.auth();
+
+export default admin;
+
--- a/backend/infra/README.md
+++ b/backend/infra/README.md
@@ -0,0 +1,94 @@
+# Database Setup
+
+## Prerequisites
+
+- PostgreSQL installed locally
+- Database created (e.g., `koin_ping_dev`)
+
+## Setup Steps
+
+### 1. Create Database
+
+```bash
+# Using psql
+createdb koin_ping_dev
+
+# Or via psql command line
+psql -U postgres
+CREATE DATABASE koin_ping_dev;
+\q
+```
+
+### 2. Set Environment Variables
+
+Create a `.env` file in the `backend/` directory:
+
+```env
+DATABASE_URL=postgresql://your_user:your_password@localhost:5432/koin_ping_dev
+```
+
+Or if using individual variables (for `infra/database.js`):
+
+```env
+DB_HOST=localhost
+DB_PORT=5432
+DB_USER=your_user
+DB_PASSWORD=your_password
+DB_NAME=koin_ping_dev
+```
+
+### 3. Run Schema
+
+```bash
+# From the backend 
+psql -d koin_ping_dev -f db/schema.sql
+
+# Or the full connection string
+psql postgresql://your_user:your_password@localhost:5432/koin_ping_dev -f db/schema.sql
+```
+
+### 4. Verify Tables
+
+```bash
+psql -d koin_ping_dev
+
+# In psql:
+\dt                    # List tables
+\d addresses          # Describe addresses table
+\d alert_rules        # Describe alert_rules table
+\d alert_events       # Describe alert_events table
+```
+
+## Tables
+
+### addresses
+- `id` - Primary key
+- `address` - Ethereum address (unique)
+- `label` - Optional display name
+- `created_at` - Timestamp
+
+### alert_rules
+- `id` - Primary key
+- `address_id` - Foreign key to addresses
+- `type` - Alert type: `incoming_tx`, `outgoing_tx`, `large_transfer`, `balance_below`
+- `threshold` - ETH amount (nullable)
+- `enabled` - Active status
+- `created_at` - Timestamp
+
+### alert_events
+- `id` - Primary key
+- `alert_rule_id` - Foreign key to alert_rules
+- `message` - Alert description
+- `address_label` - Denormalized label for display
+- `timestamp` - When alert fired
+
+## Reset Database
+
+To start fresh:
+
+```bash
+psql -d koin_ping_dev -f db/schema.sql
+```
+
+The schema includes `DROP TABLE IF EXISTS` statements for clean reruns.
+
--- a/backend/infra/add_notification_config.sql
+++ b/backend/infra/add_notification_config.sql
@@ -0,0 +1,21 @@
+
+-- Run: psql -d koin_ping_dev -f add_notification_config.sql
+
+-- Create user notification configuration tableStores notification preferences and webhook URLs for each user
+CREATE TABLE user_notification_configs (
+  user_id VARCHAR(128) PRIMARY KEY,
+  discord_webhook_url TEXT,            -- Discord webhook URL (nullable)
+  telegram_chat_id VARCHAR(128),       -- Telegram chat ID (nullable)
+  telegram_bot_token VARCHAR(255),     -- Telegram bot token (nullable, future use)
+  email VARCHAR(255),                  -- Email for notifications (nullable)
+  notification_enabled BOOLEAN DEFAULT TRUE,  -- Master on/off switch
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+-- Create index for active notifications lookup
+CREATE INDEX idx_notification_configs_enabled ON user_notification_configs(notification_enabled);
+
+-- Note: No foreign key to a users table (doesn't exist yet)
+-- user_id is the Firebase UID, validated by backend middleware
+
--- a/backend/infra/add_user_id_migration.sql
+++ b/backend/infra/add_user_id_migration.sql
@@ -0,0 +1,16 @@
+
+ALTER TABLE addresses 
+ADD COLUMN user_id VARCHAR(128);
+
+UPDATE addresses 
+SET user_id = 'legacy_user' 
+WHERE user_id IS NULL;
+
+ALTER TABLE addresses 
+ALTER COLUMN user_id SET NOT NULL;
+
+CREATE INDEX idx_addresses_user_id ON addresses(user_id);
+
+ALTER TABLE addresses DROP CONSTRAINT IF EXISTS addresses_address_key;
+
+ALTER TABLE addresses ADD CONSTRAINT addresses_user_address_unique UNIQUE (user_id, address);
--- a/backend/infra/database.js
+++ b/backend/infra/database.js
@@ -0,0 +1,32 @@
+import pg from "pg";
+import dotenv from "dotenv";
+
+dotenv.config();
+
+const { Pool } = pg;
+
+const pool = new Pool(
+  process.env.DATABASE_URL
+    ? { connectionString: process.env.DATABASE_URL }
+    : {
+        host: process.env.DB_HOST || "localhost",
+        port: process.env.DB_PORT || 5432,
+        user: process.env.DB_USER,
+        password: process.env.DB_PASSWORD,
+        database: process.env.DB_NAME,
+        max: 20,
+        idleTimeoutMillis: 30000,
+        connectionTimeoutMillis: 2000,
+      }
+);
+
+pool.on("connect", () => {
+  console.log("Connected to PostgreSQL database");
+});
+
+pool.on("error", (err) => {
+  console.error("Unexpected error on idle client", err);
+  process.exit(1);
+});
+
+export default pool;
--- a/backend/infra/schema.sql
+++ b/backend/infra/schema.sql
@@ -0,0 +1,71 @@
+
+DROP TABLE IF EXISTS alert_events CASCADE;
+DROP TABLE IF EXISTS alert_rules CASCADE;
+DROP TABLE IF EXISTS address_checkpoints CASCADE;
+DROP TABLE IF EXISTS user_notification_configs CASCADE;
+DROP TABLE IF EXISTS addresses CASCADE;
+
+CREATE TABLE addresses (
+  id SERIAL PRIMARY KEY,
+  user_id VARCHAR(128) NOT NULL,       -- Firebase user ID (multi-user support)
+  address VARCHAR(42) NOT NULL,        -- Ethereum address format (0x + 40 hex chars)
+  label VARCHAR(255),                  -- Optional human-readable label
+  created_at TIMESTAMP DEFAULT NOW(),
+  
+  -- Unique users can track the same address independently
+  UNIQUE(user_id, address)
+);
+
+
+CREATE TABLE alert_rules (
+  id SERIAL PRIMARY KEY,
+  address_id INTEGER NOT NULL REFERENCES addresses(id) ON DELETE CASCADE,
+  type VARCHAR(50) NOT NULL,           -- 'incoming_tx', 'outgoing_tx', 'large_transfer', 'balance_below'
+  threshold DECIMAL(20, 6),            -- ETH amount threshold (nullable for tx types that don't need it)
+  enabled BOOLEAN DEFAULT TRUE,
+  created_at TIMESTAMP DEFAULT NOW(),
+
+  CONSTRAINT valid_alert_type CHECK (
+    type IN ('incoming_tx', 'outgoing_tx', 'large_transfer', 'balance_below')
+  ),
+
+  CONSTRAINT positive_threshold CHECK (
+    threshold IS NULL OR threshold > 0
+  )
+);
+
+
+CREATE TABLE alert_events (
+  id SERIAL PRIMARY KEY,
+  alert_rule_id INTEGER NOT NULL REFERENCES alert_rules(id) ON DELETE CASCADE,
+  message TEXT NOT NULL,               -- Human-readable alert message
+  address_label VARCHAR(255),          -- Denormalized for display (avoids joins)
+  tx_hash VARCHAR(66),                 -- Transaction hash that triggered alert (nullable for balance_below)
+  timestamp TIMESTAMP DEFAULT NOW()
+);
+
+CREATE TABLE address_checkpoints (
+  address_id INTEGER PRIMARY KEY REFERENCES addresses(id) ON DELETE CASCADE,
+  last_checked_block INTEGER NOT NULL, -- Last block number that was checked for this address
+  last_checked_at TIMESTAMP DEFAULT NOW()
+);
+
+CREATE TABLE user_notification_configs (
+  user_id VARCHAR(128) PRIMARY KEY,
+  discord_webhook_url TEXT,            -- Discord webhook URL (nullable)
+  telegram_chat_id VARCHAR(128),       -- Telegram chat ID (nullable)
+  telegram_bot_token VARCHAR(255),     -- Telegram bot token (nullable, future use)
+  email VARCHAR(255),                  -- Email for notifications (nullable)
+  notification_enabled BOOLEAN DEFAULT TRUE,  -- Master on/off switch
+  created_at TIMESTAMP DEFAULT NOW(),
+  updated_at TIMESTAMP DEFAULT NOW()
+);
+
+-- Create indexes for common queries
+CREATE INDEX idx_addresses_user_id ON addresses(user_id);
+CREATE INDEX idx_alert_rules_address_id ON alert_rules(address_id);
+CREATE INDEX idx_alert_rules_enabled ON alert_rules(enabled);
+CREATE INDEX idx_alert_events_timestamp ON alert_events(timestamp DESC);
+CREATE INDEX idx_alert_events_alert_rule_id ON alert_events(alert_rule_id);
+CREATE INDEX idx_address_checkpoints_last_checked_at ON address_checkpoints(last_checked_at);
+CREATE INDEX idx_notification_configs_enabled ON user_notification_configs(notification_enabled);
--- a/backend/middleware/authenticate.js
+++ b/backend/middleware/authenticate.js
@@ -0,0 +1,68 @@
+
+import { auth } from '../firebase/admin.js';
+
+
+export async function authenticate(req, res, next) {
+  try {
+    // Get Authorization header
+    const authHeader = req.headers.authorization;
+    
+    if (!authHeader || !authHeader.startsWith('Bearer ')) {
+      console.log('No Authorization header or invalid format');
+      return res.status(401).json({ 
+        error: 'UNAUTHORIZED',
+        message: 'No authentication token provided' 
+      });
+    }
+
+    const token = authHeader.split('Bearer ')[1];
+    
+    if (!token) {
+      console.log('Empty token');
+      return res.status(401).json({ 
+        error: 'UNAUTHORIZED',
+        message: 'Invalid token format' 
+      });
+    }
+ 
+    console.log('Verifying Firebase token...');
+    const decodedToken = await auth.verifyIdToken(token);
+    
+    const user_id = decodedToken.uid;
+    
+    // SMOKE TEST: Console log the user_id
+    console.log('Token verified!');
+    console.log('   User ID:', user_id);
+    console.log('   Email:', decodedToken.email);
+    console.log('   Token issued at:', new Date(decodedToken.iat * 1000).toISOString());
+    
+    req.user_id = user_id;
+    req.user_email = decodedToken.email;
+    
+    next();
+    
+  } catch (error) {
+    console.error('Token verification failed:', error.message);
+    
+    // Handle specific Firebase errors
+    if (error.code === 'auth/id-token-expired') {
+      return res.status(401).json({ 
+        error: 'TOKEN_EXPIRED',
+        message: 'Authentication token has expired' 
+      });
+    }
+    
+    if (error.code === 'auth/argument-error') {
+      return res.status(401).json({ 
+        error: 'INVALID_TOKEN',
+        message: 'Invalid authentication token format' 
+      });
+    }
+    
+    return res.status(401).json({ 
+      error: 'UNAUTHORIZED',
+      message: 'Failed to verify authentication token' 
+    });
+  }
+}
+
--- a/backend/models/AddressCheckpointModel.js
+++ b/backend/models/AddressCheckpointModel.js
@@ -0,0 +1,76 @@
+import pool from '../infra/database.js';
+
+
+/**
+ * Get the last checked block number for an address
+ * @param {number} addressId - Address ID from the addresses table
+ * @returns {Promise<number|null>} Last checked block number, or null if never checked
+ */
+export async function getLastCheckedBlock(addressId) {
+  const result = await pool.query(
+    `SELECT last_checked_block
+     FROM address_checkpoints
+     WHERE address_id = $1`,
+    [addressId]
+  );
+  
+  return result.rows[0]?.last_checked_block || null;
+}
+
+/**
+ * Update the last checked block number for an address
+ * Creates a new checkpoint record if one doesn't exist
+ * @param {number} addressId - Address ID from the addresses table
+ * @param {number} blockNumber - Block number that was just checked
+ * @returns {Promise<Object>} Updated checkpoint record
+ */
+export async function updateLastCheckedBlock(addressId, blockNumber) {
+  const result = await pool.query(
+    `INSERT INTO address_checkpoints (address_id, last_checked_block, last_checked_at)
+     VALUES ($1, $2, NOW())
+     ON CONFLICT (address_id)
+     DO UPDATE SET
+       last_checked_block = $2,
+       last_checked_at = NOW()
+     RETURNING address_id, last_checked_block, last_checked_at`,
+    [addressId, blockNumber]
+  );
+  
+  return result.rows[0];
+}
+
+/**
+ * Get all address checkpoints (useful for debugging/monitoring)
+ * @returns {Promise<Array>} Array of checkpoint objects
+ */
+export async function listAll() {
+  const result = await pool.query(
+    `SELECT 
+       ac.address_id,
+       a.address,
+       a.label,
+       ac.last_checked_block,
+       ac.last_checked_at
+     FROM address_checkpoints ac
+     JOIN addresses a ON a.id = ac.address_id
+     ORDER BY ac.last_checked_at DESC`
+  );
+  
+  return result.rows;
+}
+
+/**
+ * Delete checkpoint for an address (useful when address is removed)
+ * Note: This should happen automatically via CASCADE when address is deleted
+ * @param {number} addressId - Address ID
+ * @returns {Promise<boolean>} True if deleted, false if not found
+ */
+export async function remove(addressId) {
+  const result = await pool.query(
+    `DELETE FROM address_checkpoints WHERE address_id = $1`,
+    [addressId]
+  );
+  
+  return result.rowCount > 0;
+}
+
--- a/backend/models/AddressModel.js
+++ b/backend/models/AddressModel.js
@@ -0,0 +1,84 @@
+import pool from '../infra/database.js';
+
+/**
+ * Create a new address
+ * @param {string} user_id - Firebase user ID
+ * @param {string} address - Ethereum address
+ * @param {string|null} label - Optional label
+ * @returns {Promise<Object>} Created address object
+ */
+export async function create(user_id, address, label) {
+  const result = await pool.query(
+    `INSERT INTO addresses (user_id, address, label)
+     VALUES ($1, $2, $3)
+     RETURNING id, user_id, address, label, created_at`,
+    [user_id, address, label]
+  );
+  return result.rows[0];
+}
+
+/**
+ * List all addresses for a specific user
+ * @param {string} user_id - Firebase user ID
+ * @returns {Promise<Array>} Array of address objects
+ */
+export async function listByUser(user_id) {
+  const result = await pool.query(
+    `SELECT id, address, label, created_at
+     FROM addresses
+     WHERE user_id = $1
+     ORDER BY created_at DESC`,
+    [user_id]
+  );
+  return result.rows;
+}
+
+/**
+ * List all addresses (for system use only, e.g., poller)
+ * @returns {Promise<Array>} Array of address objects
+ */
+export async function list() {
+  const result = await pool.query(
+    `SELECT id, user_id, address, label, created_at
+     FROM addresses
+     ORDER BY created_at DESC`
+  );
+  return result.rows;
+}
+
+/**
+ * Find address by ID (for specific user)
+ * @param {number} id - Address ID
+ * @param {string} user_id - Firebase user ID (for ownership verification)
+ * @returns {Promise<Object|null>} Address object or null if not found or not owned by user
+ */
+export async function findById(id, user_id = null) {
+  const query = user_id
+    ? `SELECT id, user_id, address, label, created_at
+       FROM addresses
+       WHERE id = $1 AND user_id = $2`
+    : `SELECT id, user_id, address, label, created_at
+       FROM addresses
+       WHERE id = $1`;
+  
+  const params = user_id ? [id, user_id] : [id];
+  
+  const result = await pool.query(query, params);
+  return result.rows[0] || null;
+}
+
+/**
+ * Remove address by ID (for specific user)
+ * @param {number} id - Address ID
+ * @param {string} user_id - Firebase user ID (for ownership verification)
+ * @returns {Promise<boolean>} True if deleted, false if not found or not owned by user
+ */
+export async function remove(id, user_id) {
+  const result = await pool.query(
+    `DELETE FROM addresses 
+     WHERE id = $1 AND user_id = $2`,
+    [id, user_id]
+  );
+  return result.rowCount > 0;
+}
+
--- a/backend/models/AlertEventModel.js
+++ b/backend/models/AlertEventModel.js
@@ -0,0 +1,56 @@
+import pool from '../infra/database.js';
+
+/**
+ * List recent alert events for a specific user
+ * @param {string} user_id - Firebase user ID
+ * @param {number} limit - Maximum number of events to return
+ * @returns {Promise<Array>} Array of alert event objects
+ */
+export async function listRecentByUser(user_id, limit = 20) {
+  const result = await pool.query(
+    `SELECT ae.id, ae.alert_rule_id, ae.message, ae.address_label, ae.tx_hash, ae.timestamp
+     FROM alert_events ae
+     JOIN alert_rules ar ON ar.id = ae.alert_rule_id
+     JOIN addresses a ON a.id = ar.address_id
+     WHERE a.user_id = $1
+     ORDER BY ae.timestamp DESC
+     LIMIT $2`,
+    [user_id, limit]
+  );
+  return result.rows;
+}
+
+/**
+ * List recent alert events
+ * @param {number} limit - Maximum number of event
+ * @returns {Promise<Array>} Array of alert event objects
+ */
+export async function listRecent(limit = 20) {
+  const result = await pool.query(
+    `SELECT id, alert_rule_id, message, address_label, tx_hash, timestamp
+     FROM alert_events
+     ORDER BY timestamp DESC
+     LIMIT $1`,
+    [limit]
+  );
+  return result.rows;
+}
+
+/**
+ * Create a new alert event
+ * @param {number} alertRuleId - Alert rule ID
+ * @param {string} message - Alert message
+ * @param {string|null} addressLabel - Address label (denormalized)
+ * @param {string|null} txHash - Transaction hash (optional, null for non-tx alerts)
+ * @returns {Promise<Object>} Created alert event object
+ */
+export async function create(alertRuleId, message, addressLabel, txHash = null) {
+  const result = await pool.query(
+    `INSERT INTO alert_events (alert_rule_id, message, address_label, tx_hash)
+     VALUES ($1, $2, $3, $4)
+     RETURNING id, alert_rule_id, message, address_label, tx_hash, timestamp`,
+    [alertRuleId, message, addressLabel, txHash]
+  );
+  return result.rows[0];
+}
+
--- a/backend/models/AlertRuleModel.js
+++ b/backend/models/AlertRuleModel.js
@@ -0,0 +1,92 @@
+import pool from '../infra/database.js';
+
+/**
+ * Create new alertrule
+ * @param {number} addressId - Address ID
+ * @param {string} type - Alert type
+ * @param {string|null} threshold - Threshold value (nullable)
+ * @returns {Promise<Object>} Created alert rule object
+ */
+export async function create(addressId, type, threshold) {
+  const result = await pool.query(
+    `INSERT INTO alert_rules (address_id, type, threshold, enabled)
+     VALUES ($1, $2, $3, TRUE)
+     RETURNING id, address_id, type, threshold, enabled, created_at`,
+    [addressId, type, threshold]
+  );
+  return result.rows[0];
+}
+
+/**
+ * List alert rules by address ID
+ * @param {number} addressId - Address ID
+ * @returns {Promise<Array>} Array of alert rule objects
+ */
+export async function listByAddress(addressId) {
+  const result = await pool.query(
+    `SELECT id, address_id, type, threshold, enabled, created_at
+     FROM alert_rules
+     WHERE address_id = $1
+     ORDER BY created_at DESC`,
+    [addressId]
+  );
+  return result.rows;
+}
+
+/**
+ * Find alert rule by ID
+ * @param {number} id - Alert rule ID
+ * @param {string} user_id - Optional user ID for ownership verification
+ * @returns {Promise<Object|null>} Alert rule object or null if not found/not owned
+ */
+export async function findById(id, user_id = null) {
+  let query, params;
+  
+  if (user_id) {
+    // Verify ownership 
+    query = `SELECT ar.id, ar.address_id, ar.type, ar.threshold, ar.enabled, ar.created_at
+             FROM alert_rules ar
+             JOIN addresses a ON a.id = ar.address_id
+             WHERE ar.id = $1 AND a.user_id = $2`;
+    params = [id, user_id];
+  } else {
+    query = `SELECT id, address_id, type, threshold, enabled, created_at
+             FROM alert_rules
+             WHERE id = $1`;
+    params = [id];
+  }
+  
+  const result = await pool.query(query, params);
+  return result.rows[0] || null;
+}
+
+/**
+ * Update alert rule enabled status
+ * @param {number} id - Alert rule ID
+ * @param {boolean} enabled - Enabled status
+ * @returns {Promise<Object|null>} Updated alert rule or null if not found
+ */
+export async function updateEnabled(id, enabled) {
+  const result = await pool.query(
+    `UPDATE alert_rules
+     SET enabled = $2
+     WHERE id = $1
+     RETURNING id, address_id, type, threshold, enabled, created_at`,
+    [id, enabled]
+  );
+  return result.rows[0] || null;
+}
+
+/**
+ * Remove alert rule by ID
+ * @param {number} id - Alert rule ID
+ * @returns {Promise<boolean>} True if deleted, false if not found
+ */
+export async function remove(id) {
+  const result = await pool.query(
+    `DELETE FROM alert_rules WHERE id = $1`,
+    [id]
+  );
+  return result.rowCount > 0;
+}
+
--- a/backend/models/NotificationConfigModel.js
+++ b/backend/models/NotificationConfigModel.js
@@ -0,0 +1,86 @@
+import pool from '../infra/database.js';
+
+/**
+ * Get notification config for a user
+ * @param {string} user_id - Firebase user ID
+ * @returns {Promise<Object|null>} Notification config or null if not set
+ */
+export async function getConfig(user_id) {
+  const result = await pool.query(
+    `SELECT user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token, 
+            email, notification_enabled, created_at, updated_at
+     FROM user_notification_configs
+     WHERE user_id = $1`,
+    [user_id]
+  );
+  
+  return result.rows[0] || null;
+}
+
+/**
+ * Create or update notification config for a user
+ * @param {string} user_id - Firebase user ID
+ * @param {Object} config - Notification configuration
+ * @param {string} [config.discord_webhook_url] - Discord webhook URL
+ * @param {string} [config.telegram_chat_id] - Telegram chat ID
+ * @param {string} [config.email] - Email address
+ * @param {boolean} [config.notification_enabled] - Enable/disable notifications
+ * @returns {Promise<Object>} Updated config
+ */
+export async function upsertConfig(user_id, config) {
+  const {
+    discord_webhook_url,
+    telegram_chat_id,
+    telegram_bot_token,
+    email,
+    notification_enabled = true
+  } = config;
+
+  const result = await pool.query(
+    `INSERT INTO user_notification_configs 
+      (user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token, email, notification_enabled, updated_at)
+     VALUES ($1, $2, $3, $4, $5, $6, NOW())
+     ON CONFLICT (user_id)
+     DO UPDATE SET
+       discord_webhook_url = COALESCE($2, user_notification_configs.discord_webhook_url),
+       telegram_chat_id = COALESCE($3, user_notification_configs.telegram_chat_id),
+       telegram_bot_token = COALESCE($4, user_notification_configs.telegram_bot_token),
+       email = COALESCE($5, user_notification_configs.email),
+       notification_enabled = $6,
+       updated_at = NOW()
+     RETURNING user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token, 
+               email, notification_enabled, created_at, updated_at`,
+    [user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token, email, notification_enabled]
+  );
+  
+  return result.rows[0];
+}
+
+/**
+ * Delete notification config for a user
+ * @param {string} user_id - Firebase user ID
+ * @returns {Promise<boolean>} True if deleted, false if not found
+ */
+export async function remove(user_id) {
+  const result = await pool.query(
+    `DELETE FROM user_notification_configs WHERE user_id = $1`,
+    [user_id]
+  );
+  
+  return result.rowCount > 0;
+}
+
+/**
+ * Get all users with notifications enabled (for system use)
+ * @returns {Promise<Array>} Array of user configs
+ */
+export async function listEnabled() {
+  const result = await pool.query(
+    `SELECT user_id, discord_webhook_url, telegram_chat_id, email
+     FROM user_notification_configs
+     WHERE notification_enabled = TRUE`
+  );
+  
+  return result.rows;
+}
+
--- a/backend/notifications/discordNotifier.js
+++ b/backend/notifications/discordNotifier.js
@@ -0,0 +1,114 @@
+/**
+ * https://discord.com/developers/docs/resources/webhook#execute-webhook
+ */
+
+/**
+ * Send an alert notification to webhook
+ * @param {string} webhookUrl - Discord webhook URL
+ * @param {string} message - Alert message
+ * @param {Object} metadata - Additional alert metadata
+ * @param {string} metadata.txHash - Transaction hash (nullable)
+ * @param {string} metadata.addressLabel - Address label
+ * @param {string} metadata.alertType - Alert type
+ * @param {string} metadata.address - Blockchain address
+ * @returns {Promise<boolean>} True if sent successfully, false otherwise
+ */
+export async function sendDiscordNotification(webhookUrl, message, metadata) {
+  const { txHash, addressLabel, alertType, address } = metadata;
+
+  try {
+    const payload = {
+      content: null, 
+      embeds: [
+        {
+          title: 'Koin Ping Alert',
+          description: message,
+          color: getColorForAlertType(alertType),
+          fields: [
+            {
+              name: 'Address',
+              value: addressLabel || 'Unknown',
+              inline: true,
+            },
+            {
+              name: 'Blockchain Address',
+              value: `\`${address}\``,
+              inline: false,
+            },
+          ],
+          timestamp: new Date().toISOString(),
+          footer: {
+            text: 'Koin Ping',
+          },
+        },
+      ],
+    };
+
+    if (txHash) {
+      payload.embeds[0].fields.push({
+        name: 'Transaction',
+        value: `[View on Etherscan](https://etherscan.io/tx/${txHash})`,
+        inline: false,
+      });
+    }
+
+    const response = await fetch(webhookUrl, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(payload),
+    });
+
+    if (!response.ok) {
+      const errorText = await response.text();
+      throw new Error(
+        `Discord webhook failed: HTTP ${response.status} - ${errorText}`
+      );
+    }
+
+    return true;
+  } catch (error) {
+    console.error('Failed to send Discord notification:', error.message);
+    return false;
+  }
+}
+
+/**
+ * Get Discord embed color based on alert type
+ * @param {string} alertType - Alert type
+ * @returns {number} 
+ */
+function getColorForAlertType(alertType) {
+  const colors = {
+    incoming_tx: 0x00ff00, // Green - incoming money
+    outgoing_tx: 0xff9900, // Orange - outgoing money
+    large_transfer: 0xff0000, // Red - large movement
+    balance_below: 0xff0000, // Red - low balance warning
+  };
+
+  return colors[alertType] || 0x0099ff; 
+}
+
+/**
+ * Sends a  test message to verify webhook works
+ * @param {string} webhookUrl 
+ * @returns {Promise<boolean>} 
+ */
+export async function testDiscordWebhook(webhookUrl) {
+  try {
+    const payload = {
+      content: 'Koin Ping test notification - Your Discord webhook is configured correctly!',
+    };
+
+    const response = await fetch(webhookUrl, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(payload),
+    });
+
+    return response.ok;
+  } catch (error) {
+    console.error('Discord webhook test failed:', error.message);
+    return false;
+  }
+}
+
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
--- a/backend/package.json
+++ b/backend/package.json
@@ -0,0 +1,28 @@
+{
+  "name": "backend",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "start": "node api/server.js",
+    "dev": "nodemon api/server.js",
+    "poller": "node poller/observerPoller.js",
+    "poller:dev": "nodemon poller/observerPoller.js",
+    "dev:all": "concurrently \"npm run dev\" \"npm run poller:dev\" --names \"API,POLLER\" --prefix-colors \"cyan,magenta\""
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "type": "module",
+  "dependencies": {
+    "cors": "^2.8.5",
+    "dotenv": "^17.2.3",
+    "express": "^5.2.1",
+    "firebase-admin": "^13.6.0",
+    "pg": "^8.16.3"
+  },
+  "devDependencies": {
+    "concurrently": "^9.2.1",
+    "nodemon": "^3.1.11"
+  }
+}
--- a/backend/poller/observerPoller.js
+++ b/backend/poller/observerPoller.js
@@ -0,0 +1,125 @@
+/**
+ * pure scheduling - no business logic, no DB, no blockchain details.
+ */
+
+import dotenv from 'dotenv';
+import { ObserverService } from '../services/observerService.js';
+import { EvaluatorService } from '../services/evaluatorService.js';
+import { JsonRpcEthereum } from '../protocols/ethereum/JsonRpcEthereum.js';
+
+
+dotenv.config();
+
+const ETH_RPC_URL = process.env.ETH_RPC_URL;
+const POLL_INTERVAL_MS = parseInt(process.env.POLL_INTERVAL_MS || '60000', 10);
+
+if (!ETH_RPC_URL) {
+  console.error('ERROR: ETH_RPC_URL environment variable is required');
+  console.error('Please set it in your .env file');
+  process.exit(1);
+}
+
+if (isNaN(POLL_INTERVAL_MS) || POLL_INTERVAL_MS < 1000) {
+  console.error('ERROR: POLL_INTERVAL_MS must be a number >= 1000');
+  process.exit(1);
+}
+
+const eth = new JsonRpcEthereum(ETH_RPC_URL);
+const observer = new ObserverService(eth);
+const evaluator = new EvaluatorService(eth);
+
+let isRunning = false;
+
+
+/**
+ * Sleep for specified milliseconds
+ * @param {number} ms - Milliseconds to sleep
+ * @returns {Promise<void>}
+ */
+function sleep(ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+/**
+ * Run observation cycle with error handling
+ * 
+ * @returns {Promise<void>}
+ */
+async function runCycle() {
+  try {
+    const startTime = Date.now();
+    console.log(`[${new Date().toISOString()}] Starting observation cycle...`);
+    const observations = await observer.runOnce();
+    const alertsFired = await evaluator.evaluate(observations);
+
+    const duration = Date.now() - startTime;
+    console.log(
+      `[${new Date().toISOString()}] Cycle complete: ` +
+      `${observations.length} observations, ${alertsFired} alerts fired in ${duration}ms`
+    );
+  } catch (error) {
+    console.error(`[${new Date().toISOString()}] Observation cycle failed:`, error.message);
+  }
+}
+
+async function startPolling() {
+  if (isRunning) {
+    console.warn('Poller is already running');
+    return;
+  }
+
+  isRunning = true;
+  console.log('='.repeat(60));
+  console.log('Koin Ping Observer Poller Starting');
+  console.log('='.repeat(60));
+  console.log(`RPC URL: ${ETH_RPC_URL}`);
+  console.log(`Poll Interval: ${POLL_INTERVAL_MS}ms (${POLL_INTERVAL_MS / 1000}s)`);
+  console.log('='.repeat(60));
+
+  await runCycle();
+
+  while (isRunning) {
+    await sleep(POLL_INTERVAL_MS);
+    
+    if (isRunning) {
+      await runCycle();
+    }
+  }
+
+  console.log('Poller stopped');
+}
+
+function stopPolling() {
+  if (!isRunning) {
+    return;
+  }
+
+  console.log('\n' + '='.repeat(60));
+  console.log('Shutting down poller gracefully...');
+  console.log('='.repeat(60));
+  isRunning = false;
+}
+
+// -------------------------
+// Graceful Shutdown Handlers
+// -------------------------
+
+process.on('SIGINT', () => {
+  stopPolling();
+  setTimeout(() => process.exit(0), 2000);
+});
+
+process.on('SIGTERM', () => {
+  stopPolling();
+  setTimeout(() => process.exit(0), 2000);
+});
+
+if (import.meta.url === `file://${process.argv[1]}`) {
+  startPolling().catch((error) => {
+    console.error('Fatal error in poller:', error);
+    process.exit(1);
+  });
+}
+
+export { startPolling, stopPolling };
+
--- a/backend/protocols/ethereum/EthereumObserver.js
+++ b/backend/protocols/ethereum/EthereumObserver.js
@@ -0,0 +1,61 @@
+
+/**
+ * @typedef {import('../../domain/NormalizedTx.js').NormalizedTx} NormalizedTx
+ */
+
+/**
+ * @typedef {Object} EthereumObserver
+ * @property {() => Promise<number>} getLatestBlockNumber - Get the most recent block number on the chain
+ * @property {(blockNumber: number) => Promise<NormalizedTx[]>} getBlockTransactions - Get all transactions in a specific block
+ * @property {(address: string) => Promise<string>} getBalance - Get the current balance of an address (in Wei as string)
+ */
+
+/**
+ * Validates that an object implements the EthereumObserver interface
+ * @param {any} obj - Object to validate
+ * @returns {boolean} True if object implements the interface
+ */
+export function isEthereumObserver(obj) {
+  if (!obj || typeof obj !== 'object') {
+    return false;
+  }
+
+  return (
+    typeof obj.getLatestBlockNumber === 'function' &&
+    typeof obj.getBlockTransactions === 'function' &&
+    typeof obj.getBalance === 'function'
+  );
+}
+
+/**
+ * Asserts that an object implements the EthereumObserver interface
+ * Throws an error if validation fails
+ * @param {any} obj - Object to validate
+ * @param {string} [name='object'] - Name for error messages
+ * @throws {Error} If object doesn't implement the interface
+ */
+export function assertEthereumObserver(obj, name = 'object') {
+  if (!isEthereumObserver(obj)) {
+    throw new Error(
+      `${name} must implement EthereumObserver interface ` +
+      `(getLatestBlockNumber, getBlockTransactions, getBalance)`
+    );
+  }
+}
+
+/**
+ * Example usage 
+ * 
+ * import { assertEthereumObserver } from './protocols/ethereum/EthereumObserver.js';
+ * 
+ * export function createObserverService(ethereumObserver) {
+ *   assertEthereumObserver(ethereumObserver, 'ethereumObserver');
+ *   // ... use ethereumObserver safely
+ * }
+ */
+
+export default {
+  isEthereumObserver,
+  assertEthereumObserver,
+};
+
--- a/backend/protocols/ethereum/JsonRpcEthereum.js
+++ b/backend/protocols/ethereum/JsonRpcEthereum.js
@@ -0,0 +1,159 @@
+
+import { assertEthereumObserver } from './EthereumObserver.js';
+
+/**
+ * @typedef {import('../../domain/NormalizedTx.js').NormalizedTx} NormalizedTx
+ */
+
+const RPC_TIMEOUT_MS = 30000; // 30 seconds
+
+/**
+ * JsonRpcEthereum - Concrete implementation of EthereumObserver using JSON-RPC
+ * @implements {EthereumObserver}
+ */
+export class JsonRpcEthereum {
+  /**
+   * @param {string} rpcUrl - Ethereum JSON-RPC endpoint URL
+   */
+  constructor(rpcUrl) {
+    if (!rpcUrl || typeof rpcUrl !== 'string') {
+      throw new Error('JsonRpcEthereum requires a valid RPC URL');
+    }
+    this.rpcUrl = rpcUrl;
+  }
+  /**
+   * Make a JSON-RPC call to the Ethereum node
+   * @private
+   * @param {string} method - RPC method name (e.g., 'eth_blockNumber')
+   * @param {any[]} params - Method parameters
+   * @returns {Promise<any>} RPC result
+   * @throws {Error} If RPC call fails or returns an error
+   */
+  async _callRpc(method, params = []) {
+    const controller = new AbortController();
+    const timeoutId = setTimeout(() => controller.abort(), RPC_TIMEOUT_MS);
+
+    try {
+      const response = await fetch(this.rpcUrl, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({
+          jsonrpc: '2.0',
+          id: Date.now(), 
+          method,
+          params,
+        }),
+        signal: controller.signal,
+      });
+
+      clearTimeout(timeoutId);
+
+      if (!response.ok) {
+        throw new Error(
+          `HTTP ${response.status}: ${response.statusText} for ${method}`
+        );
+      }
+
+      const payload = await response.json();
+
+      if (payload.error) {
+        throw new Error(
+          `RPC Error [${method}]: ${payload.error.message} (code: ${payload.error.code})`
+        );
+      }
+
+      return payload.result;
+    } catch (error) {
+      clearTimeout(timeoutId);
+
+      if (error.name === 'AbortError') {
+        throw new Error(`RPC timeout after ${RPC_TIMEOUT_MS}ms for ${method}`);
+      }
+
+      throw new Error(`RPC call failed [${method}]: ${error.message}`);
+    }
+  }
+
+  /**
+   * Get the latest block number on the chain
+   * @returns {Promise<number>} Current block number
+   */
+  async getLatestBlockNumber() {
+    const hexBlock = await this._callRpc('eth_blockNumber');
+    return parseInt(hexBlock, 16);
+  }
+
+  /**
+   * Get all transactions in a specific block
+   * @param {number} blockNumber - Block number to fetch
+   * @returns {Promise<NormalizedTx[]>} Array of normalized transactions
+   */
+  async getBlockTransactions(blockNumber) {
+    const hexBlockNumber = '0x' + blockNumber.toString(16);
+
+    const block = await this._callRpc('eth_getBlockByNumber', [
+      hexBlockNumber,
+      true, // true = return full transaction objects, not just hashes
+    ]);
+
+    if (!block || !block.transactions) {
+      return [];
+    }
+
+    const blockTimestamp = parseInt(block.timestamp, 16);
+
+    return block.transactions.map((tx) => ({
+      hash: tx.hash,
+      from: tx.from?.toLowerCase() || '',
+      to: tx.to?.toLowerCase() || null, // null for contract creation
+      value: this._hexToDecimalString(tx.value), 
+      blockNumber: parseInt(tx.blockNumber, 16),
+      blockTimestamp: blockTimestamp,
+    }));
+  }
+
+  /**
+   * Get the current balance of an address
+   * @param {string} address - Ethereum address
+   * @returns {Promise<string>} Balance in Wei as decimal string
+   */
+  async getBalance(address) {
+    const balanceHex = await this._callRpc('eth_getBalance', [
+      address,
+      'latest',
+    ]);
+
+    return this._hexToDecimalString(balanceHex);
+  }
+
+  /**
+   * Convert hex string to decimal string (for large numbers)
+   * @private
+   * @param {string} hexValue - Hex value (with or without 0x prefix)
+   * @returns {string} 
+   */
+  _hexToDecimalString(hexValue) {
+    if (!hexValue || hexValue === '0x' || hexValue === '0x0') {
+      return '0';
+    }
+    
+    try {
+      return BigInt(hexValue).toString();
+    } catch (error) {
+      throw new Error(`Invalid hex value: ${hexValue}`);
+    }
+  }
+}
+
+/**
+ * @param {string} rpcUrl - Ethereum JSON-RPC endpoint URL
+ * @returns {JsonRpcEthereum}
+ */
+export function createJsonRpcEthereum(rpcUrl) {
+  const instance = new JsonRpcEthereum(rpcUrl);
+  
+  // Validate that it implements the interface
+  assertEthereumObserver(instance, 'JsonRpcEthereum');
+  
+  return instance;
+}
--- a/backend/services/evaluatorService.js
+++ b/backend/services/evaluatorService.js
@@ -0,0 +1,258 @@
+
+import { assertEthereumObserver } from '../protocols/ethereum/EthereumObserver.js';
+import * as AlertRuleModel from '../models/AlertRuleModel.js';
+import * as AlertEventModel from '../models/AlertEventModel.js';
+import * as AddressModel from '../models/AddressModel.js';
+import * as NotificationConfigModel from '../models/NotificationConfigModel.js';
+import { ethToWei, weiGreaterThanOrEqual, weiLessThan, formatWeiAsEth } from '../shared/weiConverter.js';
+import { sendDiscordNotification } from '../notifications/discordNotifier.js';
+
+/**
+ * @typedef {import('../domain/ObservedTx.js').ObservedTx} ObservedTx
+ * @typedef {import('../protocols/ethereum/EthereumObserver.js').EthereumObserver} EthereumObserver
+ */
+
+export class EvaluatorService {
+  /**
+   * @param {EthereumObserver} ethObserver - Implementation of EthereumObserver interface
+   */
+  constructor(ethObserver) {
+    assertEthereumObserver(ethObserver, 'ethObserver');
+    this.eth = ethObserver;
+  }
+
+  /**
+   * Evaluate all observations against their associated alert rules
+   * @param {ObservedTx[]} observations 
+   * @returns {Promise<number>} 
+   */
+  async evaluate(observations) {
+    let alertsFired = 0;
+
+    for (const obs of observations) {
+      try {
+        const fired = await this._evaluateObservation(obs);
+        alertsFired += fired;
+      } catch (error) {
+        console.error(
+          `Error evaluating observation for address ID ${obs.addressId}:`,
+          error.message
+        );
+        // Continue processing other observations - tbd
+      }
+    }
+
+    return alertsFired;
+  }
+
+  /**
+   * Evaluate a single observation against all rules
+   * @private
+   * @param {ObservedTx} obs 
+   * @returns {Promise<number>}
+   */
+  async _evaluateObservation(obs) {
+    const rules = await AlertRuleModel.listByAddress(obs.addressId);
+    let alertsFired = 0;
+
+    for (const rule of rules) {
+      // Skip disabled 
+      if (!rule.enabled) {
+        continue;
+      }
+
+      const matches = await this._ruleMatches(rule, obs);
+      
+      if (matches) {
+        await this._fireAlert(rule, obs);
+        alertsFired++;
+      }
+    }
+
+    return alertsFired;
+  }
+
+  /**
+   * Fire an alert by creating an alert event
+   * @private
+   * @param {Object} rule - Alert rule that matched
+   * @param {ObservedTx} obs - Observed transaction that triggered it
+   * @returns {Promise<void>}
+   */
+  async _fireAlert(rule, obs) {
+    const address = await AddressModel.findById(obs.addressId);
+    const addressLabel = address?.label || address?.address || 'Unknown';
+
+    const message = this._buildMessage(rule, obs);
+    const txHash = obs.hash;
+    await AlertEventModel.create(rule.id, message, addressLabel, txHash);
+
+    console.log(
+      `[ALERT FIRED] Rule ${rule.id} (${rule.type}) - ${message} - TX: ${txHash}`
+    );
+
+    // Send Discord notification if configured
+    try {
+      const user_id = address.user_id;
+      const notificationConfig = await NotificationConfigModel.getConfig(user_id);
+
+      if (
+        notificationConfig?.discord_webhook_url &&
+        notificationConfig.notification_enabled
+      ) {
+        const sent = await sendDiscordNotification(
+          notificationConfig.discord_webhook_url,
+          message,
+          {
+            txHash,
+            addressLabel,
+            alertType: rule.type,
+            address: address.address,
+          }
+        );
+
+        if (sent) {
+          console.log(`Discord notification sent to user ${user_id}`);
+        } else {
+          console.warn(`Discord notification failed for user ${user_id}`);
+        }
+      }
+    } catch (notificationError) {
+      // Don't fail the alert if notification fails
+      console.error(
+        `Failed to send Discord notification:`,
+        notificationError.message
+      );
+    }
+  }
+
+  /**
+   * Check if a rule matches an observation
+   * @private
+   * @param {Object} rule - Alert rule to evaluate
+   * @param {ObservedTx} obs - Observed transaction
+   * @returns {Promise<boolean>} True if rule conditions are met
+   */
+  async _ruleMatches(rule, obs) {
+    switch (rule.type) {
+      case 'incoming_tx':
+        return this._matchesIncomingTx(obs);
+
+      case 'outgoing_tx':
+        return this._matchesOutgoingTx(obs);
+
+      case 'large_transfer':
+        return this._matchesLargeTransfer(rule, obs);
+
+      case 'balance_below':
+        return await this._matchesBalanceBelow(rule, obs);
+
+      default:
+        console.warn(`Unknown rule type: ${rule.type}`);
+        return false;
+    }
+  }
+
+  /**
+   * Match incoming transaction rule
+   * @private
+   */
+  _matchesIncomingTx(obs) {
+    return obs.direction === 'incoming';
+  }
+
+  /**
+   * Match outgoing transaction rule
+   * @private
+   */
+  _matchesOutgoingTx(obs) {
+    return obs.direction === 'outgoing';
+  }
+
+  /**
+   * Match large transfer rule
+   * @private
+   * 
+   * IMPORTANT: Threshold is stored as ETH in DB, but we compare in Wei
+   * for precision. Both incoming and outgoing transfers are checked.
+   */
+  _matchesLargeTransfer(rule, obs) {
+    if (!rule.threshold) {
+      return false;
+    }
+
+    const thresholdWei = ethToWei(Number(rule.threshold));
+    const transferValueWei = obs.value;
+
+    return weiGreaterThanOrEqual(transferValueWei, thresholdWei);
+  }
+
+  /**
+   *  balance below threshold rule
+   * @private
+   * 
+   * OPTIMIZATION: Only check balance after outgoing transactions
+   * (incoming transactions increase balance, so can't trigger this alert)
+   * 
+   * IMPORTANT: Threshold stored as ETH in DB, but compared in Wei.
+   */
+  async _matchesBalanceBelow(rule, obs) {
+    if (!rule.threshold) {
+      return false;
+    }
+
+    if (obs.direction !== 'outgoing') {
+      return false;
+    }
+
+    const address = await AddressModel.findById(obs.addressId);
+    if (!address) {
+      console.warn(`Address ID ${obs.addressId} not found`);
+      return false;
+    }
+
+    const balanceWei = await this.eth.getBalance(address.address);
+
+    // Convert ETH threshold from DB to Wei for comparison
+    const thresholdWei = ethToWei(Number(rule.threshold));
+
+
+    return weiLessThan(balanceWei, thresholdWei);
+  }
+
+  /**
+   * Build a human-readable alert message
+   * @private
+   * @param {Object} rule - Alert rule that matched
+   * @param {ObservedTx} obs - Observed transaction
+   * @returns {string} Human-readable message
+   */
+  _buildMessage(rule, obs) {
+    switch (rule.type) {
+      case 'incoming_tx':
+        return `Incoming transaction: ${formatWeiAsEth(obs.value)} received`;
+
+      case 'outgoing_tx':
+        return `Outgoing transaction: ${formatWeiAsEth(obs.value)} sent`;
+
+      case 'large_transfer':
+        return `Large transfer detected: ${formatWeiAsEth(obs.value)} (threshold: ${rule.threshold} ETH)`;
+
+      case 'balance_below':
+        return `Balance dropped below threshold of ${rule.threshold} ETH`;
+
+      default:
+        return 'Alert triggered';
+    }
+  }
+}
+
+/**
+ * Factory function to create an EvaluatorService instance
+ * @param {EthereumObserver} ethObserver - Implementation of EthereumObserver interface
+ * @returns {EvaluatorService}
+ */
+export function createEvaluatorService(ethObserver) {
+  return new EvaluatorService(ethObserver);
+}
+
--- a/backend/services/observerService.js
+++ b/backend/services/observerService.js
@@ -0,0 +1,158 @@
+
+import { assertEthereumObserver } from '../protocols/ethereum/EthereumObserver.js';
+import * as AddressModel from '../models/AddressModel.js';
+import * as CheckpointModel from '../models/AddressCheckpointModel.js';
+
+/**
+ * @typedef {import('../domain/NormalizedTx.js').NormalizedTx} NormalizedTx
+ * @typedef {import('../domain/ObservedTx.js').ObservedTx} ObservedTx
+ * @typedef {import('../protocols/ethereum/EthereumObserver.js').EthereumObserver} EthereumObserver
+ */
+
+// Safety limit: maximum blocks to process per address per run
+// Prevents overwhelming RPC endpoints and ensures bounded execution time
+const MAX_BLOCKS_PER_RUN = 100;
+
+
+export class ObserverService {
+  /**
+   * @param {EthereumObserver} ethObserver - Implementation of EthereumObserver interface
+   */
+  constructor(ethObserver) {
+    assertEthereumObserver(ethObserver, 'ethObserver');
+    this.eth = ethObserver;
+  }
+
+  /**
+   * Run one observation cycle across all tracked addresses
+   * 
+   * 
+   * @returns {Promise<ObservedTx[]>} All observations from this cycle
+   */
+  async runOnce() {
+    const addresses = await AddressModel.list();
+    
+    if (addresses.length === 0) {
+      return [];
+    }
+
+    const latestBlock = await this.eth.getLatestBlockNumber();
+    const observations = [];
+
+    for (const address of addresses) {
+      try {
+        const addressObservations = await this._observeAddress(address, latestBlock);
+        observations.push(...addressObservations);
+      } catch (error) {
+        console.error(`Error observing address ${address.address}:`, error);
+
+      }
+    }
+
+    return observations;
+  }
+
+  /**
+   * Observe a single address for activity
+   * @private
+   * @param {Object} address - Address record from database
+   * @param {number} latestBlock - Current latest block number
+   * @returns {Promise<ObservedTx[]>} Observations for this address
+   */
+  async _observeAddress(address, latestBlock) {
+    const lastChecked = await CheckpointModel.getLastCheckedBlock(address.id);
+    
+    const startBlock = this._getStartBlock(lastChecked, latestBlock);
+    const endBlock = this._getEndBlock(startBlock, latestBlock);
+
+    // No new blocks to check
+    if (startBlock > endBlock) {
+      return [];
+    }
+
+    const observations = [];
+
+    for (let blockNumber = startBlock; blockNumber <= endBlock; blockNumber++) {
+      const blockTxs = await this.eth.getBlockTransactions(blockNumber);
+      const relevantTxs = this._filterRelevantTransactions(blockTxs, address.address);
+
+      for (const tx of relevantTxs) {
+        observations.push(this._createObservedTx(tx, address));
+      }
+    }
+
+    await CheckpointModel.updateLastCheckedBlock(address.id, endBlock);
+
+    return observations;
+  }
+
+  /**
+   * Determine starting block for observation
+   * @private
+   * @param {number|null} lastChecked - Last checked block, or null if never checked
+   * @param {number} latestBlock - Current latest block
+   * @returns {number} Block number to start from
+   */
+  _getStartBlock(lastChecked, latestBlock) {
+    if (lastChecked === null) {
+      return latestBlock;
+    }
+    return lastChecked + 1;
+  }
+
+  /**
+   * Determine ending block for observation (respects MAX_BLOCKS_PER_RUN)
+   * @private
+   * @param {number} startBlock 
+   * @param {number} latestBlock 
+   * @returns {number} 
+   */
+  _getEndBlock(startBlock, latestBlock) {
+    return Math.min(startBlock + MAX_BLOCKS_PER_RUN - 1, latestBlock);
+  }
+
+  /**
+   * Filter transactions to only those involving the tracked address
+   * @private
+   * @param {NormalizedTx[]} transactions 
+   * @param {string} trackedAddress 
+   * @returns {NormalizedTx[]} 
+   */
+  _filterRelevantTransactions(transactions, trackedAddress) {
+    const addressLower = trackedAddress.toLowerCase();
+    
+    return transactions.filter((tx) => {
+      const fromMatch = tx.from?.toLowerCase() === addressLower;
+      const toMatch = tx.to?.toLowerCase() === addressLower;
+      return fromMatch || toMatch;
+    });
+  }
+
+  /**
+   * Create an ObservedTx with direction metadata
+   * @private
+   * @param {NormalizedTx} tx - Normalized transaction
+   * @param {Object} address - Address record from database
+   * @returns {ObservedTx} Transaction with observation metadata
+   */
+  _createObservedTx(tx, address) {
+    const addressLower = address.address.toLowerCase();
+    const direction = tx.to?.toLowerCase() === addressLower ? 'incoming' : 'outgoing';
+
+    return {
+      ...tx,
+      addressId: address.id,
+      direction,
+    };
+  }
+}
+
+/**
+ * Factory  to create an ObserverService instance
+ * @param {EthereumObserver} ethObserver - Implementation of EthereumObserver interface
+ * @returns {ObserverService}
+ */
+export function createObserverService(ethObserver) {
+  return new ObserverService(ethObserver);
+}
+
--- a/backend/shared/weiConverter.js
+++ b/backend/shared/weiConverter.js
@@ -0,0 +1,95 @@
+
+
+const WEI_PER_ETH = 1000000000000000000n; // 10^18 Wei = 1 ETH
+
+/**
+ * Convert Wei (as string) to ETH (as number)
+ * Use for display purposes only, not for calculations
+ * @param {string} weiString - Wei value as string
+ * @returns {number} ETH value as number
+ */
+export function weiToEth(weiString) {
+  if (!weiString || weiString === '0') {
+    return 0;
+  }
+  
+  try {
+    const wei = BigInt(weiString);
+    // Convert to number (safe for display values)
+    return Number(wei) / Number(WEI_PER_ETH);
+  } catch (error) {
+    throw new Error(`Invalid Wei value: ${weiString}`);
+  }
+}
+
+/**
+ * Convert ETH (as number) to Wei (as string)
+ * Use when converting DB thresholds for comparison
+ * @param {number} eth - ETH value as number
+ * @returns {string} Wei value as string
+ */
+export function ethToWei(eth) {
+  if (typeof eth !== 'number' || isNaN(eth)) {
+    throw new Error(`Invalid ETH value: ${eth}`);
+  }
+  
+  if (eth === 0) {
+    return '0';
+  }
+  
+  // Convert to string with fixed precision to avoid floating point issues
+  const ethString = eth.toFixed(18); // Max precision
+  const [whole, decimal = ''] = ethString.split('.');
+  
+
+  const wholePart = BigInt(whole) * WEI_PER_ETH;
+  const decimalPart = BigInt(decimal.padEnd(18, '0'));
+  
+  return (wholePart + decimalPart).toString();
+}
+
+/**
+ * Compare two Wei values
+ * @param {string} weiA 
+ * @param {string} weiB 
+ * @returns {number} 
+ */
+export function compareWei(weiA, weiB) {
+  const a = BigInt(weiA);
+  const b = BigInt(weiB);
+  
+  if (a < b) return -1;
+  if (a > b) return 1;
+  return 0;
+}
+
+/**
+ * Check if Wei value A is greater than or equal to Wei value B
+ * @param {string} weiA - First Wei value as string
+ * @param {string} weiB - Second Wei value as string
+ * @returns {boolean}
+ */
+export function weiGreaterThanOrEqual(weiA, weiB) {
+  return BigInt(weiA) >= BigInt(weiB);
+}
+
+/**
+ * Check if Wei value A is less than Wei value B
+ * @param {string} weiA 
+ * @param {string} weiB 
+ * @returns {boolean}
+ */
+export function weiLessThan(weiA, weiB) {
+  return BigInt(weiA) < BigInt(weiB);
+}
+
+/**
+ * @param {string} weiString 
+ * @param {number} decimals - Number of decimal places (default: 4)
+ * @returns {string}
+ */
+export function formatWeiAsEth(weiString, decimals = 4) {
+  const eth = weiToEth(weiString);
+  return `${eth.toFixed(decimals)} ETH`;
+}
+
--- a/frontend/.gitignore
+++ b/frontend/.gitignore
@@ -0,0 +1,8 @@
+node_modules/
+.env
+*.log
+.DS_Store
+dist/
+build/
+.vite/
+src/secrets.js
--- a/frontend/README.md
+++ b/frontend/README.md
@@ -0,0 +1,38 @@
+# Koin Ping Frontend
+
+React + Vite frontend for the on-chain monitoring and alerting system.
+
+## Getting Started
+
+1. Install dependencies:
+   ```bash
+   npm install
+   ```
+
+2. Run the development server:
+   ```bash
+   npm run dev
+   ```
+
+3. Build for production:
+   ```bash
+   npm run build
+   ```
+
+4. Preview production build:
+   ```bash
+   npm run preview
+   ```
+
+## Project Structure
+
+- `src/api/` - API calls to backend
+- `src/components/` - Reusable UI components
+- `src/pages/` - Top-level page components
+- `src/utils/` - Utility functions
+- `public/` - Static assets
+
+## Development
+
+The frontend runs on port 3000 and proxies API requests to the backend running on port 5000.
+
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Koin Ping - On-Chain Monitoring</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.jsx"></script>
+  </body>
+</html>
+
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -0,0 +1,31 @@
+{
+  "name": "frontend",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  },
+  "keywords": [
+    "cryptocurrency",
+    "event moitoring"
+  ],
+  "author": "Steven Jannette",
+  "license": "MIT",
+  "type": "module",
+  "dependencies": {
+    "firebase": "^12.7.0",
+    "react": "^19.2.3",
+    "react-dom": "^19.2.3",
+    "react-router-dom": "^7.11.0"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.7",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^5.1.2",
+    "typescript": "^5.9.3",
+    "vite": "^7.3.0"
+  }
+}
--- a/frontend/src/App.jsx
+++ b/frontend/src/App.jsx
@@ -0,0 +1,62 @@
+import { Routes, Route, Link, Navigate } from "react-router-dom";
+import { useAuth } from "./contexts/AuthContext";
+import Login from "./pages/Login";
+import Signup from "./pages/Signup";
+import Addresses from "./pages/Addresses";
+import Alerts from "./pages/Alerts";
+import AlertHistory from "./pages/AlertHistory";
+
+export default function App() {
+  const { currentUser, logout } = useAuth();
+
+  // Show login/signup routes if not authenticated
+  if (!currentUser) {
+    return (
+      <Routes>
+        <Route path="/login" element={<Login />} />
+        <Route path="/signup" element={<Signup />} />
+        <Route path="*" element={<Navigate to="/login" />} />
+      </Routes>
+    );
+  }
+
+  // Show main app if authenticated
+  return (
+    <div style={{ padding: "1rem" }}>
+      <nav style={{ marginBottom: "1rem", display: "flex", justifyContent: "space-between", alignItems: "center" }}>
+        <div>
+          <Link to="/addresses">Addresses</Link>{" | "}
+          <Link to="/alerts">Alerts</Link>{" | "}
+          <Link to="/history">History</Link>
+        </div>
+        <div style={{ display: "flex", alignItems: "center", gap: "1rem" }}>
+          <span style={{ fontSize: "0.9rem", color: "#999" }}>
+            {currentUser.email}
+          </span>
+          <button
+            onClick={logout}
+            style={{
+              padding: "0.5rem 1rem",
+              fontSize: "0.9rem",
+              backgroundColor: "#333",
+              color: "white",
+              border: "1px solid #555",
+              borderRadius: "4px",
+              cursor: "pointer"
+            }}
+          >
+            Logout
+          </button>
+        </div>
+      </nav>
+
+      <Routes>
+        <Route path="/" element={<Addresses />} />
+        <Route path="/addresses" element={<Addresses />} />
+        <Route path="/alerts" element={<Alerts />} />
+        <Route path="/history" element={<AlertHistory />} />
+        <Route path="*" element={<Navigate to="/addresses" />} />
+      </Routes>
+    </div>
+  );
+}
--- a/frontend/src/api/addresses.jsx
+++ b/frontend/src/api/addresses.jsx
@@ -0,0 +1,113 @@
+// API client for address management
+
+import { getAuthHeaders, getAuthHeadersSimple } from './authHeaders';
+
+const API_BASE = '/api';
+
+/**
+ * Create a new blockchain address to monitor
+ * @param {Object} data - Address data
+ * @param {string} data.address - Blockchain address (0x...)
+ * @param {string} [data.label] - Optional label for the address
+ * @returns {Promise<Object>} Created address with id and metadata
+ */
+export async function createAddress(data) {
+  try {
+  const headers = await getAuthHeaders();
+  const response = await fetch(`${API_BASE}/addresses`, {
+    method: 'POST',
+    headers: headers,
+    body: JSON.stringify(data)
+  });
+  
+  if (!response.ok) {
+      // Try to parse error response, but handle if it's not JSON
+      let errorMessage = 'Failed to create address';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        // If JSON parse fails, use status text
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    // Handle network errors
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Get all tracked addresses
+ * @returns {Promise<Array>} List of all addresses
+ */
+export async function getAddresses() {
+  try {
+  const headers = await getAuthHeadersSimple();
+  const response = await fetch(`${API_BASE}/addresses`, {
+    headers: headers
+  });
+  
+  if (!response.ok) {
+      // Try to parse error response, but handle if it's not JSON
+      let errorMessage = 'Failed to fetch addresses';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        // If JSON parse fails, use status text
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    // Handle network errors or JSON parse errors
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Delete a tracked address
+ * @param {number} addressId - Address ID to delete
+ * @returns {Promise<void>}
+ */
+export async function deleteAddress(addressId) {
+  try {
+  const headers = await getAuthHeadersSimple();
+  const response = await fetch(`${API_BASE}/addresses/${addressId}`, {
+    method: 'DELETE',
+    headers: headers
+  });
+  
+  if (!response.ok && response.status !== 204) {
+      // Try to parse error response, but handle if it's not JSON
+      let errorMessage = 'Failed to delete address';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        // If JSON parse fails, use status text
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+    }
+  } catch (error) {
+    // Handle network errors
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
--- a/frontend/src/api/alertEvents.jsx
+++ b/frontend/src/api/alertEvents.jsx
@@ -0,0 +1,36 @@
+// API client for alert event history
+
+import { getAuthHeadersSimple } from './authHeaders';
+
+const API_BASE = '/api';
+
+/**
+ * Get all alert events (history)
+ * @returns {Promise<Array>} List of alert events, sorted by most recent first
+ */
+export async function getAlertEvents() {
+  try {
+  const headers = await getAuthHeadersSimple();
+  const response = await fetch(`${API_BASE}/alert-events`, {
+    headers: headers
+  });
+  
+  if (!response.ok) {
+      let errorMessage = 'Failed to fetch alert events';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
--- a/frontend/src/api/alerts.jsx
+++ b/frontend/src/api/alerts.jsx
@@ -0,0 +1,150 @@
+// API client for alert rule management
+
+import { getAuthHeaders, getAuthHeadersSimple } from './authHeaders';
+
+const API_BASE = '/api';
+
+/**
+ * Alert types supported by the system
+ */
+export const ALERT_TYPES = {
+  INCOMING_TX: 'incoming_tx',
+  OUTGOING_TX: 'outgoing_tx',
+  LARGE_TRANSFER: 'large_transfer',
+  BALANCE_BELOW: 'balance_below'
+};
+
+/**
+ * Create a new alert rule for an address
+ * @param {number} addressId - Address ID
+ * @param {Object} data - Alert rule data
+ * @param {string} data.type - Alert type (one of ALERT_TYPES)
+ * @param {string} [data.threshold] - Threshold value (required for large_transfer and balance_below)
+ * @returns {Promise<Object>} Created alert rule
+ */
+export async function createAlert(addressId, data) {
+  try {
+  const headers = await getAuthHeaders();
+  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
+    method: 'POST',
+    headers: headers,
+    body: JSON.stringify(data)
+  });
+  
+  if (!response.ok) {
+      let errorMessage = 'Failed to create alert rule';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Get all alert rules for an address
+ * @param {number} addressId - Address ID
+ * @returns {Promise<Array>} List of alert rules
+ */
+export async function getAlerts(addressId) {
+  try {
+  const headers = await getAuthHeadersSimple();
+  const response = await fetch(`${API_BASE}/addresses/${addressId}/alerts`, {
+    headers: headers
+  });
+  
+  if (!response.ok) {
+      let errorMessage = 'Failed to fetch alert rules';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Enable or disable an alert rule
+ * @param {number} alertId - Alert rule ID
+ * @param {boolean} enabled - Whether the alert should be enabled
+ * @returns {Promise<Object>} Updated alert rule
+ */
+export async function updateAlertStatus(alertId, enabled) {
+  try {
+  const headers = await getAuthHeaders();
+  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+    method: 'PATCH',
+    headers: headers,
+    body: JSON.stringify({ enabled })
+  });
+  
+  if (!response.ok) {
+      let errorMessage = 'Failed to update alert rule';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+  }
+  
+  return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Delete an alert rule
+ * @param {number} alertId - Alert rule ID
+ * @returns {Promise<void>}
+ */
+export async function deleteAlert(alertId) {
+  try {
+  const headers = await getAuthHeadersSimple();
+  const response = await fetch(`${API_BASE}/alerts/${alertId}`, {
+    method: 'DELETE',
+    headers: headers
+  });
+  
+  if (!response.ok && response.status !== 204) {
+      let errorMessage = 'Failed to delete alert rule';
+      try {
+    const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+    }
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
--- a/frontend/src/api/authHeaders.js
+++ b/frontend/src/api/authHeaders.js
@@ -0,0 +1,47 @@
+/**
+ * Auth Headers Helper
+ * 
+ * Provides authentication headers for API calls
+ * Includes Firebase ID token in Authorization header
+ */
+
+import { auth } from '../firebase/config';
+
+/**
+ * Get headers with authentication token
+ * @returns {Promise<Object>} Headers object with Authorization
+ */
+export async function getAuthHeaders() {
+  const currentUser = auth.currentUser;
+  
+  if (!currentUser) {
+    throw new Error('No authenticated user');
+  }
+
+  // Get Firebase ID token
+  const token = await currentUser.getIdToken();
+
+  return {
+    'Content-Type': 'application/json',
+    'Authorization': `Bearer ${token}`
+  };
+}
+
+/**
+ * Get headers for non-JSON requests (e.g., DELETE with no body)
+ * @returns {Promise<Object>} Headers object with Authorization
+ */
+export async function getAuthHeadersSimple() {
+  const currentUser = auth.currentUser;
+  
+  if (!currentUser) {
+    throw new Error('No authenticated user');
+  }
+
+  const token = await currentUser.getIdToken();
+
+  return {
+    'Authorization': `Bearer ${token}`
+  };
+}
+
--- a/frontend/src/api/notificationConfig.jsx
+++ b/frontend/src/api/notificationConfig.jsx
@@ -0,0 +1,100 @@
+// API client for notification configuration
+
+import { getAuthHeaders } from './authHeaders';
+
+const API_BASE = '/api';
+
+/**
+ * Get notification configuration for current user
+ * @returns {Promise<Object>} Notification config
+ */
+export async function getNotificationConfig() {
+  try {
+    const headers = await getAuthHeaders();
+    const response = await fetch(`${API_BASE}/notification-config`, {
+      headers: headers
+    });
+    
+    if (!response.ok) {
+      let errorMessage = 'Failed to fetch notification config';
+      try {
+        const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+    }
+    
+    return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Update notification configuration
+ * @param {Object} config - Configuration to update
+ * @param {string} [config.discord_webhook_url] - Discord webhook URL
+ * @param {string} [config.telegram_chat_id] - Telegram chat ID
+ * @param {string} [config.email] - Email address
+ * @param {boolean} [config.notification_enabled] - Enable/disable notifications
+ * @returns {Promise<Object>} Updated config
+ */
+export async function updateNotificationConfig(config) {
+  try {
+    const headers = await getAuthHeaders();
+    const response = await fetch(`${API_BASE}/notification-config`, {
+      method: 'PUT',
+      headers: headers,
+      body: JSON.stringify(config)
+    });
+    
+    if (!response.ok) {
+      let errorMessage = 'Failed to update notification config';
+      try {
+        const error = await response.json();
+        errorMessage = error.message || errorMessage;
+      } catch {
+        errorMessage = `Server error: ${response.status} ${response.statusText}`;
+      }
+      throw new Error(errorMessage);
+    }
+    
+    return response.json();
+  } catch (error) {
+    if (error.message.includes('fetch')) {
+      throw new Error('Cannot connect to server. Is the backend running?');
+    }
+    throw error;
+  }
+}
+
+/**
+ * Test a Discord webhook URL
+ * Sends a test message to verify the webhook works
+ * @param {string} webhookUrl - Discord webhook URL to test
+ * @returns {Promise<boolean>} True if test successful
+ */
+export async function testDiscordWebhook(webhookUrl) {
+  try {
+    const payload = {
+      content: 'Koin Ping test notification - Your Discord webhook is configured correctly!',
+    };
+
+    const response = await fetch(webhookUrl, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(payload)
+    });
+
+    return response.ok;
+  } catch (error) {
+    console.error('Discord webhook test failed:', error);
+    return false;
+  }
+}
+
--- a/frontend/src/api/status.jsx
+++ b/frontend/src/api/status.jsx
@@ -0,0 +1,18 @@
+// API client for system status
+
+const API_BASE = '/api';
+
+/**
+ * Get system status including latest processed block and health
+ * @returns {Promise<Object>} System status
+ */
+export async function getSystemStatus() {
+  const response = await fetch(`${API_BASE}/status`);
+  
+  if (!response.ok) {
+    const error = await response.json();
+    throw new Error(error.message || 'Failed to fetch system status');
+  }
+  
+  return response.json();
+}
--- a/frontend/src/components/AddressForm.jsx
+++ b/frontend/src/components/AddressForm.jsx
@@ -0,0 +1,45 @@
+import { useState } from "react";
+import Input from "./Input";
+import Button from "./Button";
+
+export default function AddressForm({ onSubmit }) {
+  const [address, setAddress] = useState("");
+  const [label, setLabel] = useState("");
+
+  const canSubmit = address.trim().length > 0;
+
+  function handleSubmit(e) {
+    e.preventDefault();
+    if (!canSubmit) return;
+
+    onSubmit({
+      address: address.trim(),
+      label: label.trim(),
+    });
+
+    setAddress("");
+    setLabel("");
+  }
+
+  return (
+    <form onSubmit={handleSubmit}>
+      <Input
+        label="Blockchain Address"
+        value={address}
+        onChange={setAddress}
+        placeholder="0x..."
+      />
+
+      <Input
+        label="Label (optional)"
+        value={label}
+        onChange={setLabel}
+        placeholder="Treasury, Cold Wallet, etc."
+      />
+
+      <Button type="submit" disabled={!canSubmit}>
+        Add Address
+      </Button>
+    </form>
+  );
+}
--- a/frontend/src/components/AlertForm.jsx
+++ b/frontend/src/components/AlertForm.jsx
@@ -0,0 +1,71 @@
+import { useState } from "react";
+import Input from "./Input";
+import Button from "./Button";
+
+const ALERT_TYPES = [
+  { value: "incoming_tx", label: "Incoming transaction" },
+  { value: "outgoing_tx", label: "Outgoing transaction" },
+  { value: "large_transfer", label: "Large transfer" },
+  { value: "balance_below", label: "Balance below threshold" },
+];
+
+export default function AlertForm({ onSubmit }) {
+  const [type, setType] = useState("incoming_tx");
+  const [threshold, setThreshold] = useState("");
+
+  const needsThreshold =
+    type === "large_transfer" || type === "balance_below";
+
+  const canSubmit = needsThreshold
+    ? threshold.trim() !== "" && 
+      !isNaN(Number(threshold)) && 
+      Number(threshold) > 0
+    : true;
+
+  function handleSubmit(e) {
+    e.preventDefault();
+    if (!canSubmit) return;
+
+    onSubmit({
+      type,
+      threshold: needsThreshold ? threshold : undefined,
+    });
+
+    setThreshold("");
+  }
+
+  return (
+    <form onSubmit={handleSubmit}>
+      <div style={{ marginBottom: "1rem" }}>
+        {ALERT_TYPES.map((opt) => (
+          <label key={opt.value} style={{ display: "block" }}>
+            <input
+              type="radio"
+              name="alertType"
+              value={opt.value}
+              checked={type === opt.value}
+              onChange={() => setType(opt.value)}
+            />
+            {" "}{opt.label}
+          </label>
+        ))}
+      </div>
+
+      {needsThreshold && (
+        <Input
+          label="Amount (ETH)"
+          type="number"
+          step="0.000001"
+          min="0"
+          value={threshold}
+          onChange={setThreshold}
+          placeholder="e.g. 10"
+        />
+      )}
+
+      <Button type="submit" disabled={!canSubmit}>
+        Create Alert
+      </Button>
+    </form>
+  );
+}
--- a/frontend/src/components/Button.jsx
+++ b/frontend/src/components/Button.jsx
@@ -0,0 +1,23 @@
+export default function Button({
+    children,
+    onClick,
+    disabled = false,
+    type = "button",
+  }) {
+    return (
+      <button
+        type={type}
+        onClick={onClick}
+        disabled={disabled}
+        style={{
+          padding: "0.5rem 1rem",
+          fontSize: "1rem",
+          cursor: disabled ? "not-allowed" : "pointer",
+          opacity: disabled ? 0.6 : 1,
+        }}
+      >
+        {children}
+      </button>
+    );
+  }
+  
--- a/frontend/src/components/Input.jsx
+++ b/frontend/src/components/Input.jsx
@@ -0,0 +1,33 @@
+export default function Input({
+    label,
+    type = "text",
+    value,
+    onChange,
+    placeholder,
+    step,
+    min,
+    disabled = false,
+  }) {
+    return (
+      <label style={{ display: "block", marginBottom: "1rem" }}>
+        <div style={{ marginBottom: "0.25rem", fontSize: "0.9rem" }}>
+          {label}
+        </div>
+        <input
+          type={type}
+          value={value}
+          placeholder={placeholder}
+          step={step}
+          min={min}
+          disabled={disabled}
+          onChange={(e) => onChange(e.target.value)}
+          style={{
+            width: "100%",
+            padding: "0.5rem",
+            fontSize: "1rem",
+          }}
+        />
+      </label>
+    );
+  }
+  
--- a/frontend/src/contexts/AuthContext.jsx
+++ b/frontend/src/contexts/AuthContext.jsx
@@ -0,0 +1,107 @@
+/**
+ * AuthContext - Firebase Authentication State Management
+ * 
+ * Provides authentication state and methods throughout the app
+ */
+
+import { createContext, useContext, useEffect, useState } from 'react';
+import { 
+  createUserWithEmailAndPassword,
+  signInWithEmailAndPassword,
+  signOut,
+  onAuthStateChanged
+} from 'firebase/auth';
+import { auth } from '../firebase/config';
+
+const AuthContext = createContext();
+
+/**
+ * Hook to access auth context
+ * @returns {Object} Auth context value
+ */
+export function useAuth() {
+  const context = useContext(AuthContext);
+  if (!context) {
+    throw new Error('useAuth must be used within AuthProvider');
+  }
+  return context;
+}
+
+/**
+ * AuthProvider - Wraps app and provides auth state
+ */
+export function AuthProvider({ children }) {
+  const [currentUser, setCurrentUser] = useState(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(null);
+
+  /**
+   * Sign up with email and password
+   */
+  async function signup(email, password) {
+    try {
+      setError(null);
+      const result = await createUserWithEmailAndPassword(auth, email, password);
+      return result.user;
+    } catch (err) {
+      setError(err.message);
+      throw err;
+    }
+  }
+
+  /**
+   * Log in with email and password
+   */
+  async function login(email, password) {
+    try {
+      setError(null);
+      const result = await signInWithEmailAndPassword(auth, email, password);
+      return result.user;
+    } catch (err) {
+      setError(err.message);
+      throw err;
+    }
+  }
+
+  /**
+   * Log out current user
+   */
+  async function logout() {
+    try {
+      setError(null);
+      await signOut(auth);
+    } catch (err) {
+      setError(err.message);
+      throw err;
+    }
+  }
+
+  /**
+   * Listen for auth state changes
+   */
+  useEffect(() => {
+    const unsubscribe = onAuthStateChanged(auth, (user) => {
+      setCurrentUser(user);
+      setLoading(false);
+    });
+
+    // Cleanup subscription
+    return unsubscribe;
+  }, []);
+
+  const value = {
+    currentUser,
+    signup,
+    login,
+    logout,
+    error,
+    loading
+  };
+
+  return (
+    <AuthContext.Provider value={value}>
+      {!loading && children}
+    </AuthContext.Provider>
+  );
+}
+
--- a/frontend/src/firebase/config.js
+++ b/frontend/src/firebase/config.js
@@ -0,0 +1,30 @@
+
+import { initializeApp } from 'firebase/app';
+import { getAuth } from 'firebase/auth';
+import {
+    firebaseApiKey,
+    firebaseAuthDomain,
+    firebaseProjectId,
+    firebaseStorageBucket,
+    firebaseMessagingSenderId,
+    firebaseAppId,
+    firebaseMeasurementId
+} from '../secrets.js';
+
+
+const firebaseConfig = {
+    apiKey: firebaseApiKey,
+    authDomain: firebaseAuthDomain,
+    projectId: firebaseProjectId,
+    storageBucket: firebaseStorageBucket,
+    messagingSenderId: firebaseMessagingSenderId,
+    appId: firebaseAppId,
+    measurementId: firebaseMeasurementId
+  };
+
+const app = initializeApp(firebaseConfig);
+
+export const auth = getAuth(app);
+
+export default app;
+
--- a/frontend/src/main.jsx
+++ b/frontend/src/main.jsx
@@ -0,0 +1,15 @@
+import React from "react";
+import ReactDOM from "react-dom/client";
+import { BrowserRouter } from "react-router-dom";
+import { AuthProvider } from "./contexts/AuthContext";
+import App from "./App";
+
+ReactDOM.createRoot(document.getElementById("root")).render(
+  <React.StrictMode>
+    <BrowserRouter>
+      <AuthProvider>
+        <App />
+      </AuthProvider>
+    </BrowserRouter>
+  </React.StrictMode>
+);
--- a/frontend/src/pages/Addresses.jsx
+++ b/frontend/src/pages/Addresses.jsx
@@ -0,0 +1,83 @@
+import { useState, useEffect } from "react";
+import AddressForm from "../components/AddressForm";
+import { getAddresses, createAddress } from "../api/addresses";
+
+export default function Addresses() {
+  const [addresses, setAddresses] = useState([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(null);
+
+  // Load addresses on mount
+  useEffect(() => {
+    async function fetchAddresses() {
+      try {
+        setLoading(true);
+        const data = await getAddresses();
+        setAddresses(data);
+      } catch (err) {
+        setError(err.message);
+        console.error("Failed to fetch addresses:", err);
+      } finally {
+        setLoading(false);
+      }
+    }
+
+    fetchAddresses();
+  }, []);
+
+  // Handle new address submission
+  async function handleAddressSubmit(data) {
+    try {
+      const newAddress = await createAddress(data);
+      // Append new address to state
+      setAddresses((prev) => [...prev, newAddress]);
+      setError(null); // Clear any previous errors
+    } catch (err) {
+      setError(err.message);
+      console.error("Failed to create address:", err);
+    }
+  }
+
+  return (
+    <div style={{ maxWidth: "800px", margin: "0 auto", padding: "2rem" }}>
+      <h1>Tracked Addresses</h1>
+
+      <div style={{ marginBottom: "2rem" }}>
+        <AddressForm onSubmit={handleAddressSubmit} />
+      </div>
+
+      <div>
+        <h2>Existing Addresses</h2>
+        {loading && <p>Loading addresses...</p>}
+        {error && <p style={{ color: "red" }}>Error: {error}</p>}
+        {!loading && !error && addresses.length === 0 && (
+          <p style={{ color: "#666" }}>
+            No addresses tracked yet. Add one above to get started.
+          </p>
+        )}
+        {addresses.length > 0 && (
+          <ul style={{ listStyle: "none", padding: 0 }}>
+            {addresses.map((addr, index) => (
+              <li
+                key={addr.id || index}
+                style={{
+                  padding: "1rem",
+                  marginBottom: "0.5rem",
+                  border: "1px solid #ddd",
+                  borderRadius: "4px",
+                }}
+              >
+                <div style={{ fontWeight: "bold", marginBottom: "0.25rem" }}>
+                  {addr.label || "Unlabeled"}
+                </div>
+                <div style={{ fontFamily: "monospace", fontSize: "0.9rem" }}>
+                  {addr.address}
+                </div>
+              </li>
+            ))}
+          </ul>
+        )}
+      </div>
+    </div>
+  );
+}
--- a/frontend/src/pages/AlertHistory.jsx
+++ b/frontend/src/pages/AlertHistory.jsx
@@ -0,0 +1,74 @@
+import { useState, useEffect } from "react";
+import { getAlertEvents } from "../api/alertEvents";
+
+export default function AlertHistory() {
+  const [alertEvents, setAlertEvents] = useState([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(null);
+
+  // Fetch alert events on mount
+  useEffect(() => {
+    async function fetchAlertEvents() {
+      try {
+        setLoading(true);
+        const data = await getAlertEvents();
+        setAlertEvents(data);
+      } catch (err) {
+        setError(err.message);
+        console.error("Failed to fetch alert events:", err);
+      } finally {
+        setLoading(false);
+      }
+    }
+
+    fetchAlertEvents();
+  }, []);
+
+  if (loading) {
+    return <div style={{ padding: "2rem" }}>Loading...</div>;
+  }
+
+  if (error) {
+    return <div style={{ padding: "2rem", color: "red" }}>Error: {error}</div>;
+  }
+
+  return (
+    <div style={{ maxWidth: "800px", margin: "0 auto", padding: "2rem" }}>
+      <h1>Recent Alerts</h1>
+
+      {alertEvents.length === 0 ? (
+        <p style={{ color: "#666" }}>No alerts yet</p>
+      ) : (
+        <ul style={{ listStyle: "none", padding: 0 }}>
+          {alertEvents.map((event) => (
+            <li
+              key={event.id}
+              style={{
+                padding: "1rem",
+                marginBottom: "0.75rem",
+                border: "1px solid #ddd",
+                borderRadius: "4px",
+              }}
+            >
+              <div style={{ marginBottom: "0.5rem" }}>{event.message}</div>
+              {event.address_label && (
+                <div style={{ fontSize: "0.9rem", color: "#666", marginBottom: "0.25rem" }}>
+                  Address: {event.address_label}
+                </div>
+              )}
+              <small style={{ color: "#999" }}>
+                {formatTimestamp(event.timestamp)}
+              </small>
+            </li>
+          ))}
+        </ul>
+      )}
+    </div>
+  );
+}
+
+// Helper to format timestamp for display
+function formatTimestamp(timestamp) {
+  const date = new Date(timestamp);
+  return date.toLocaleString();
+}
--- a/frontend/src/pages/Alerts.jsx
+++ b/frontend/src/pages/Alerts.jsx
@@ -0,0 +1,471 @@
+import { useState, useEffect } from "react";
+import AlertForm from "../components/AlertForm";
+import Button from "../components/Button";
+import Input from "../components/Input";
+import { getAddresses } from "../api/addresses";
+import { getAlerts, createAlert, updateAlertStatus, deleteAlert } from "../api/alerts";
+import { getNotificationConfig, updateNotificationConfig, testDiscordWebhook } from "../api/notificationConfig";
+
+export default function Alerts() {
+  const [addresses, setAddresses] = useState([]);
+  const [selectedAddressId, setSelectedAddressId] = useState(null);
+  const [alerts, setAlerts] = useState([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(null);
+  
+  // Notification config state
+  const [notificationConfig, setNotificationConfig] = useState(null);
+  const [discordWebhookUrl, setDiscordWebhookUrl] = useState('');
+  const [notificationEnabled, setNotificationEnabled] = useState(true);
+  const [notificationLoading, setNotificationLoading] = useState(false);
+  const [notificationError, setNotificationError] = useState(null);
+  const [notificationSuccess, setNotificationSuccess] = useState(null);
+  const [testingWebhook, setTestingWebhook] = useState(false);
+
+  // Load addresses and notification config on mount
+  useEffect(() => {
+    async function fetchData() {
+      try {
+        setLoading(true);
+        
+        // Fetch addresses
+        const addressData = await getAddresses();
+        setAddresses(addressData);
+        if (addressData.length > 0) {
+          setSelectedAddressId(addressData[0].id);
+        }
+        
+        // Fetch notification config
+        const configData = await getNotificationConfig();
+        setNotificationConfig(configData);
+        setDiscordWebhookUrl(configData.discord_webhook_url || '');
+        setNotificationEnabled(configData.notification_enabled !== false);
+      } catch (err) {
+        setError(err.message);
+        console.error("Failed to fetch data:", err);
+      } finally {
+        setLoading(false);
+      }
+    }
+
+    fetchData();
+  }, []);
+
+  // Load alerts when address is selected
+  useEffect(() => {
+    if (!selectedAddressId) {
+      setAlerts([]);
+      return;
+    }
+
+    async function fetchAlerts() {
+      try {
+        const data = await getAlerts(selectedAddressId);
+        setAlerts(data);
+        setError(null); // Clear any previous errors
+      } catch (err) {
+        setError(err.message);
+        console.error("Failed to fetch alerts:", err);
+      }
+    }
+
+    fetchAlerts();
+  }, [selectedAddressId]);
+
+  // Handle new alert submission
+  async function handleAlertSubmit(data) {
+    if (!selectedAddressId) return;
+
+    try {
+      const newAlert = await createAlert(selectedAddressId, data);
+      setAlerts((prev) => [...prev, newAlert]);
+      setError(null); // Clear any previous errors
+    } catch (err) {
+      setError(err.message);
+      console.error("Failed to create alert:", err);
+    }
+  }
+
+  // Toggle alert enabled/disabled
+  async function handleToggleAlert(alertId, currentStatus) {
+    try {
+      const updated = await updateAlertStatus(alertId, !currentStatus);
+      setAlerts((prev) =>
+        prev.map((alert) => (alert.id === alertId ? updated : alert))
+      );
+      setError(null); // Clear any previous errors
+    } catch (err) {
+      setError(err.message);
+      console.error("Failed to update alert:", err);
+    }
+  }
+
+  // Delete alert
+  async function handleDeleteAlert(alertId) {
+    try {
+      await deleteAlert(alertId);
+      setAlerts((prev) => prev.filter((alert) => alert.id !== alertId));
+      setError(null); // Clear any previous errors
+    } catch (err) {
+      setError(err.message);
+      console.error("Failed to delete alert:", err);
+    }
+  }
+
+  // Save notification config
+  async function handleSaveNotificationConfig() {
+    try {
+      setNotificationLoading(true);
+      setNotificationError(null);
+      setNotificationSuccess(null);
+
+      const config = {
+        discord_webhook_url: discordWebhookUrl || null,
+        notification_enabled: notificationEnabled,
+      };
+
+      const updated = await updateNotificationConfig(config);
+      setNotificationConfig(updated);
+      setNotificationSuccess('Notification settings saved!');
+      
+      // Clear success message after 3 seconds
+      setTimeout(() => setNotificationSuccess(null), 3000);
+    } catch (err) {
+      setNotificationError(err.message);
+      console.error("Failed to save notification config:", err);
+    } finally {
+      setNotificationLoading(false);
+    }
+  }
+
+  // Test Discord webhook
+  async function handleTestWebhook() {
+    if (!discordWebhookUrl) {
+      setNotificationError('Please enter a Discord webhook URL first');
+      return;
+    }
+
+    try {
+      setTestingWebhook(true);
+      setNotificationError(null);
+      setNotificationSuccess(null);
+
+      const success = await testDiscordWebhook(discordWebhookUrl);
+      
+      if (success) {
+        setNotificationSuccess('Test notification sent! Check your Discord channel.');
+        setTimeout(() => setNotificationSuccess(null), 5000);
+      } else {
+        setNotificationError('Test failed. Check your webhook URL.');
+      }
+    } catch (err) {
+      setNotificationError('Test failed: ' + err.message);
+    } finally {
+      setTestingWebhook(false);
+    }
+  }
+
+  const selectedAddress = addresses.find((a) => a.id === selectedAddressId);
+
+  if (loading) {
+    return <div style={{ padding: "2rem" }}>Loading addresses...</div>;
+  }
+
+  if (addresses.length === 0) {
+    return (
+      <div style={{ padding: "2rem" }}>
+        <p>No addresses tracked yet. Add an address first to create alerts.</p>
+      </div>
+    );
+  }
+
+  return (
+    <div style={{ maxWidth: "1400px", margin: "0 auto", padding: "2rem" }}>
+      <h1 style={{ marginBottom: "2rem" }}>Alert Rules & Notifications</h1>
+
+      {/* Two-column layout */}
+      <div style={{ display: "grid", gridTemplateColumns: "1fr 1fr", gap: "2rem" }}>
+        
+        {/* LEFT COLUMN: Alert Rules */}
+        <div>
+          <h2 style={{ marginTop: 0 }}>Alert Rules</h2>
+          
+          {/* Address selector */}
+          <div style={{ marginBottom: "2rem" }}>
+            <label style={{ display: "block", marginBottom: "0.5rem" }}>
+              <strong>Select Address:</strong>
+            </label>
+            <select
+              value={selectedAddressId || ""}
+              onChange={(e) => setSelectedAddressId(Number(e.target.value))}
+              style={{
+                width: "100%",
+                padding: "0.5rem",
+                fontSize: "1rem",
+                backgroundColor: "#1a1a1a",
+                border: "1px solid #444",
+                borderRadius: "4px",
+                color: "white"
+              }}
+            >
+              {addresses.map((addr) => (
+                <option key={addr.id} value={addr.id}>
+                  {addr.label || "Unlabeled"} - {addr.address}
+                </option>
+              ))}
+            </select>
+          </div>
+
+          {selectedAddress && (
+            <>
+              {/* Current address info */}
+              <div
+                style={{
+                  padding: "1rem",
+                  marginBottom: "2rem",
+                  backgroundColor: "#2a2a2a",
+                  borderRadius: "4px",
+                  border: "1px solid #444"
+                }}
+              >
+                <div style={{ fontSize: "0.9rem", color: "#999" }}>
+                  Managing alerts for:
+                </div>
+                <div style={{ fontWeight: "bold", marginTop: "0.25rem" }}>
+                  {selectedAddress.label || "Unlabeled"}
+                </div>
+                <div style={{ fontFamily: "monospace", fontSize: "0.9rem", color: "#999" }}>
+                  {selectedAddress.address}
+                </div>
+              </div>
+
+              {/* Alert creation form */}
+              <div style={{ marginBottom: "2rem" }}>
+                <h3>Create New Alert</h3>
+                <AlertForm onSubmit={handleAlertSubmit} />
+              </div>
+
+              {/* Existing alerts list */}
+              <div>
+                <h3>Active Alert Rules</h3>
+                {error && <p style={{ color: "red" }}>Error: {error}</p>}
+                {alerts.length === 0 ? (
+                  <p style={{ color: "#666" }}>
+                    No alert rules defined yet. Create one above.
+                  </p>
+                ) : (
+                  <ul style={{ listStyle: "none", padding: 0 }}>
+                    {alerts.map((alert) => (
+                      <li
+                        key={alert.id}
+                        style={{
+                          padding: "1rem",
+                          marginBottom: "0.5rem",
+                          border: "1px solid #444",
+                          borderRadius: "4px",
+                          backgroundColor: "#2a2a2a",
+                          opacity: alert.enabled ? 1 : 0.6,
+                        }}
+                      >
+                        <div
+                          style={{
+                            display: "flex",
+                            justifyContent: "space-between",
+                            alignItems: "flex-start",
+                          }}
+                        >
+                          <div style={{ flex: 1 }}>
+                            <div style={{ fontWeight: "bold", marginBottom: "0.25rem" }}>
+                              {formatAlertType(alert.type)}
+                            </div>
+                            {alert.threshold && (
+                              <div style={{ fontSize: "0.9rem", color: "#999" }}>
+                                Threshold: {alert.threshold} ETH
+                              </div>
+                            )}
+                            <div style={{ fontSize: "0.85rem", color: "#666", marginTop: "0.25rem" }}>
+                              Status: {alert.enabled ? "Enabled" : "Disabled"}
+                            </div>
+                          </div>
+                          <div style={{ display: "flex", gap: "0.5rem" }}>
+                            <Button
+                              onClick={() => handleToggleAlert(alert.id, alert.enabled)}
+                            >
+                              {alert.enabled ? "Disable" : "Enable"}
+                            </Button>
+                            <Button onClick={() => handleDeleteAlert(alert.id)}>
+                              Delete
+                            </Button>
+                          </div>
+                        </div>
+                      </li>
+                    ))}
+                  </ul>
+                )}
+              </div>
+            </>
+          )}
+        </div>
+
+        {/* RIGHT COLUMN: Notification Settings */}
+        <div>
+          <h2 style={{ marginTop: 0 }}>Notification Settings</h2>
+          
+          {notificationSuccess && (
+            <div style={{
+              padding: '0.75rem',
+              marginBottom: '1rem',
+              backgroundColor: '#00ff0020',
+              border: '1px solid #00ff00',
+              borderRadius: '4px',
+              color: '#00ff00'
+            }}>
+              {notificationSuccess}
+            </div>
+          )}
+
+          {notificationError && (
+            <div style={{
+              padding: '0.75rem',
+              marginBottom: '1rem',
+              backgroundColor: '#ff000020',
+              border: '1px solid #ff0000',
+              borderRadius: '4px',
+              color: '#ff6666'
+            }}>
+              {notificationError}
+            </div>
+          )}
+
+          {/* Master toggle */}
+          <div style={{ marginBottom: '2rem', padding: '1rem', backgroundColor: '#f5f5f5', borderRadius: '4px' }}>
+            <label style={{ display: 'flex', alignItems: 'center', cursor: 'pointer' }}>
+              <input
+                type="checkbox"
+                checked={notificationEnabled}
+                onChange={(e) => setNotificationEnabled(e.target.checked)}
+                style={{ marginRight: '0.5rem', width: '18px', height: '18px' }}
+              />
+              <span style={{ fontWeight: 'bold' }}>Enable Notifications</span>
+            </label>
+            <div style={{ fontSize: '0.85rem', color: '#666', marginTop: '0.5rem', marginLeft: '26px' }}>
+              Master switch for all notification channels
+            </div>
+          </div>
+
+          {/* Discord Section */}
+          <div style={{ marginBottom: '2rem' }}>
+            <h3 style={{ marginBottom: '1rem' }}>Discord</h3>
+            
+            <div style={{ marginBottom: '1rem' }}>
+              <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+                Discord Webhook URL
+              </label>
+              <input
+                type="text"
+                value={discordWebhookUrl}
+                onChange={(e) => setDiscordWebhookUrl(e.target.value)}
+                placeholder="https://discord.com/api/webhooks/..."
+                style={{
+                  width: '100%',
+                  padding: '0.5rem',
+                  fontSize: '1rem',
+                  backgroundColor: '#1a1a1a',
+                  border: '1px solid #444',
+                  borderRadius: '4px',
+                  color: 'white',
+                  fontFamily: 'monospace',
+                  fontSize: '0.9rem'
+                }}
+              />
+              <div style={{ fontSize: '0.85rem', color: '#999', marginTop: '0.5rem' }}>
+                <a 
+                  href="https://support.discord.com/hc/en-us/articles/228383668-Intro-to-Webhooks" 
+                  target="_blank" 
+                  rel="noopener noreferrer"
+                  style={{ color: '#0066cc' }}
+                >
+                  How to get a Discord webhook URL
+                </a>
+              </div>
+            </div>
+
+            <div style={{ display: 'flex', gap: '0.5rem' }}>
+              <button
+                onClick={handleSaveNotificationConfig}
+                disabled={notificationLoading}
+                style={{
+                  padding: '0.75rem 1.5rem',
+                  fontSize: '1rem',
+                  backgroundColor: notificationLoading ? '#333' : '#0066cc',
+                  color: 'white',
+                  border: 'none',
+                  borderRadius: '4px',
+                  cursor: notificationLoading ? 'not-allowed' : 'pointer'
+                }}
+              >
+                {notificationLoading ? 'Saving...' : 'Save Settings'}
+              </button>
+
+              <button
+                onClick={handleTestWebhook}
+                disabled={testingWebhook || !discordWebhookUrl}
+                style={{
+                  padding: '0.75rem 1.5rem',
+                  fontSize: '1rem',
+                  backgroundColor: testingWebhook || !discordWebhookUrl ? '#333' : '#28a745',
+                  color: 'white',
+                  border: 'none',
+                  borderRadius: '4px',
+                  cursor: testingWebhook || !discordWebhookUrl ? 'not-allowed' : 'pointer'
+                }}
+              >
+                {testingWebhook ? 'Testing...' : 'Test Webhook'}
+              </button>
+            </div>
+          </div>
+
+          {/* Telegram Section (Coming Soon) */}
+          <div style={{ marginBottom: '2rem', opacity: 0.5 }}>
+            <h3 style={{ marginBottom: '1rem' }}>Telegram</h3>
+            <div style={{ 
+              padding: '1rem', 
+              backgroundColor: '#333', 
+              borderRadius: '4px',
+              color: '#999',
+              textAlign: 'center'
+            }}>
+              Coming Soon
+            </div>
+          </div>
+
+          {/* Email Section (Coming Soon) */}
+          <div style={{ opacity: 0.5 }}>
+            <h3 style={{ marginBottom: '1rem' }}>Email</h3>
+            <div style={{ 
+              padding: '1rem', 
+              backgroundColor: '#333', 
+              borderRadius: '4px',
+              color: '#999',
+              textAlign: 'center'
+            }}>
+              Coming Soon
+            </div>
+          </div>
+        </div>
+
+      </div>
+    </div>
+  );
+}
+
+// Helper to format alert type for display
+function formatAlertType(type) {
+  const labels = {
+    incoming_tx: "Incoming transaction",
+    outgoing_tx: "Outgoing transaction",
+    large_transfer: "Large transfer",
+    balance_below: "Balance below threshold",
+  };
+  return labels[type] || type;
+}
--- a/frontend/src/pages/Login.jsx
+++ b/frontend/src/pages/Login.jsx
@@ -0,0 +1,143 @@
+/**
+ * Login Page
+ * 
+ * Allows existing users to sign in with email and password
+ */
+
+import { useState } from 'react';
+import { Link, useNavigate } from 'react-router-dom';
+import { useAuth } from '../contexts/AuthContext';
+
+export default function Login() {
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [error, setError] = useState('');
+  const [loading, setLoading] = useState(false);
+  
+  const { login } = useAuth();
+  const navigate = useNavigate();
+
+  async function handleSubmit(e) {
+    e.preventDefault();
+
+    // Validation
+    if (!email || !password) {
+      setError('Please fill in all fields');
+      return;
+    }
+
+    try {
+      setError('');
+      setLoading(true);
+      await login(email, password);
+      navigate('/addresses'); // Redirect to main app
+    } catch (err) {
+      setError('Failed to log in: ' + err.message);
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <div style={{ 
+      maxWidth: '400px', 
+      margin: '4rem auto', 
+      padding: '2rem',
+      border: '1px solid #333',
+      borderRadius: '8px'
+    }}>
+      <h1 style={{ marginBottom: '2rem', textAlign: 'center' }}>
+        Koin Ping - Login
+      </h1>
+
+      {error && (
+        <div style={{ 
+          padding: '0.75rem', 
+          marginBottom: '1rem', 
+          backgroundColor: '#ff000020',
+          border: '1px solid #ff0000',
+          borderRadius: '4px',
+          color: '#ff6666'
+        }}>
+          {error}
+        </div>
+      )}
+
+      <form onSubmit={handleSubmit}>
+        <div style={{ marginBottom: '1rem' }}>
+          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+            Email
+          </label>
+          <input
+            type="email"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+            disabled={loading}
+            style={{
+              width: '100%',
+              padding: '0.5rem',
+              fontSize: '1rem',
+              backgroundColor: '#1a1a1a',
+              border: '1px solid #444',
+              borderRadius: '4px',
+              color: 'white'
+            }}
+            required
+          />
+        </div>
+
+        <div style={{ marginBottom: '1.5rem' }}>
+          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+            Password
+          </label>
+          <input
+            type="password"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+            disabled={loading}
+            style={{
+              width: '100%',
+              padding: '0.5rem',
+              fontSize: '1rem',
+              backgroundColor: '#1a1a1a',
+              border: '1px solid #444',
+              borderRadius: '4px',
+              color: 'white'
+            }}
+            required
+          />
+        </div>
+
+        <button
+          type="submit"
+          disabled={loading}
+          style={{
+            width: '100%',
+            padding: '0.75rem',
+            fontSize: '1rem',
+            backgroundColor: loading ? '#333' : '#0066cc',
+            color: 'white',
+            border: 'none',
+            borderRadius: '4px',
+            cursor: loading ? 'not-allowed' : 'pointer'
+          }}
+        >
+          {loading ? 'Logging in...' : 'Log In'}
+        </button>
+      </form>
+
+      <div style={{ marginTop: '1.5rem', textAlign: 'center' }}>
+        <p style={{ color: '#999' }}>
+          Don't have an account?{' '}
+          <Link 
+            to="/signup" 
+            style={{ color: '#0066cc', textDecoration: 'none' }}
+          >
+            Sign up here
+          </Link>
+        </p>
+      </div>
+    </div>
+  );
+}
+
--- a/frontend/src/pages/Signup.jsx
+++ b/frontend/src/pages/Signup.jsx
@@ -0,0 +1,185 @@
+/**
+ * Signup Page
+ * 
+ * Allows new users to create an account with email and password
+ */
+
+import { useState } from 'react';
+import { Link, useNavigate } from 'react-router-dom';
+import { useAuth } from '../contexts/AuthContext';
+
+export default function Signup() {
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [confirmPassword, setConfirmPassword] = useState('');
+  const [error, setError] = useState('');
+  const [loading, setLoading] = useState(false);
+  
+  const { signup } = useAuth();
+  const navigate = useNavigate();
+
+  async function handleSubmit(e) {
+    e.preventDefault();
+
+    // Validation
+    if (!email || !password || !confirmPassword) {
+      setError('Please fill in all fields');
+      return;
+    }
+
+    if (password !== confirmPassword) {
+      setError('Passwords do not match');
+      return;
+    }
+
+    if (password.length < 6) {
+      setError('Password must be at least 6 characters');
+      return;
+    }
+
+    try {
+      setError('');
+      setLoading(true);
+      await signup(email, password);
+      navigate('/addresses'); // Auto-login and redirect
+    } catch (err) {
+      // Firebase-specific error messages
+      if (err.code === 'auth/email-already-in-use') {
+        setError('Email already in use. Try logging in instead.');
+      } else if (err.code === 'auth/invalid-email') {
+        setError('Invalid email address');
+      } else if (err.code === 'auth/weak-password') {
+        setError('Password is too weak');
+      } else {
+        setError('Failed to create account: ' + err.message);
+      }
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <div style={{ 
+      maxWidth: '400px', 
+      margin: '4rem auto', 
+      padding: '2rem',
+      border: '1px solid #333',
+      borderRadius: '8px'
+    }}>
+      <h1 style={{ marginBottom: '2rem', textAlign: 'center' }}>
+        Koin Ping - Sign Up
+      </h1>
+
+      {error && (
+        <div style={{ 
+          padding: '0.75rem', 
+          marginBottom: '1rem', 
+          backgroundColor: '#ff000020',
+          border: '1px solid #ff0000',
+          borderRadius: '4px',
+          color: '#ff6666'
+        }}>
+          {error}
+        </div>
+      )}
+
+      <form onSubmit={handleSubmit}>
+        <div style={{ marginBottom: '1rem' }}>
+          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+            Email
+          </label>
+          <input
+            type="email"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+            disabled={loading}
+            style={{
+              width: '100%',
+              padding: '0.5rem',
+              fontSize: '1rem',
+              backgroundColor: '#1a1a1a',
+              border: '1px solid #444',
+              borderRadius: '4px',
+              color: 'white'
+            }}
+            required
+          />
+        </div>
+
+        <div style={{ marginBottom: '1rem' }}>
+          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+            Password
+          </label>
+          <input
+            type="password"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+            disabled={loading}
+            style={{
+              width: '100%',
+              padding: '0.5rem',
+              fontSize: '1rem',
+              backgroundColor: '#1a1a1a',
+              border: '1px solid #444',
+              borderRadius: '4px',
+              color: 'white'
+            }}
+            required
+          />
+        </div>
+
+        <div style={{ marginBottom: '1.5rem' }}>
+          <label style={{ display: 'block', marginBottom: '0.5rem' }}>
+            Confirm Password
+          </label>
+          <input
+            type="password"
+            value={confirmPassword}
+            onChange={(e) => setConfirmPassword(e.target.value)}
+            disabled={loading}
+            style={{
+              width: '100%',
+              padding: '0.5rem',
+              fontSize: '1rem',
+              backgroundColor: '#1a1a1a',
+              border: '1px solid #444',
+              borderRadius: '4px',
+              color: 'white'
+            }}
+            required
+          />
+        </div>
+
+        <button
+          type="submit"
+          disabled={loading}
+          style={{
+            width: '100%',
+            padding: '0.75rem',
+            fontSize: '1rem',
+            backgroundColor: loading ? '#333' : '#0066cc',
+            color: 'white',
+            border: 'none',
+            borderRadius: '4px',
+            cursor: loading ? 'not-allowed' : 'pointer'
+          }}
+        >
+          {loading ? 'Creating account...' : 'Sign Up'}
+        </button>
+      </form>
+
+      <div style={{ marginTop: '1.5rem', textAlign: 'center' }}>
+        <p style={{ color: '#999' }}>
+          Already have an account?{' '}
+          <Link 
+            to="/login" 
+            style={{ color: '#0066cc', textDecoration: 'none' }}
+          >
+            Log in here
+          </Link>
+        </p>
+      </div>
+    </div>
+  );
+}
+
--- a/frontend/tsconfig.json
+++ b/frontend/tsconfig.json
@@ -0,0 +1,25 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "useDefineForClassFields": true,
+    "lib": ["ES2020", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    /* Linting */
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true
+  },
+  "include": ["src"]
+}
+
--- a/frontend/vite.config.js
+++ b/frontend/vite.config.js
@@ -0,0 +1,17 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+// https://vitejs.dev/config/
+export default defineConfig({
+  plugins: [react()],
+  server: {
+    port: 3000,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:3001',
+        changeOrigin: true,
+      },
+    },
+  },
+})
+