backend_design.txt

The backend will be a Python Flask server that interacts with the Ethereum blockchain and serves API endpoints for the frontend. Key components:

1. Flask server setup:
   - Import necessary libraries (Flask, web3, etc.)
   - Initialize Flask app

2. Web3 integration:
   - Connect to Ethereum network using Web3.py
   - Function to validate Ethereum addresses

3. API endpoints:
   - GET /api/balance/<address>: Retrieve ETH balance for given address
   - GET /api/transactions/<address>: Fetch list of transactions for given address

4. Transaction processing:
   - Function to fetch and process transaction data
   - Pagination support for large transaction lists

5. Error handling:
   - Custom error responses for invalid addresses, network issues, etc.

6. CORS support:
   - Enable CORS to allow frontend requests

7. Environment variables:
   - Store sensitive data (e.g., Ethereum node URL) in environment variables

8. Serve static files:
   - Serve the HTML/CSS/JS files for the frontend

The server will run on localhost:5000 and provide the necessary API endpoints for the frontend to interact with the Ethereum blockchain.