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Build a crypto wallet checker

Written by

Bernardo Palos

in

To build a crypto wallet checker, you can create a simple web application that allows users to enter a wallet address and check its balance and recent transactions. Below is a functional prototype using Node.js with Express.js, and a front-end using HTML + JavaScript. This example uses Etherscan API for Ethereum wallet checking. You can adapt it for Bitcoin or other blockchains by changing the API.

Features

  • Input Ethereum wallet address

  • Validate address format

  • Fetch balance and recent transactions from Etherscan

  • Display results in the browser

Prerequisites

Folder Structure

pgsql
crypto-wallet-checker/
├── public/
│   └── index.html
├── server.js
├── package.json
└── .env

1. package.json

json
{
  "name": "crypto-wallet-checker",
  "version": "1.0.0",
  "description": "Simple Ethereum wallet checker",
  "main": "server.js",
  "scripts": {
    "start": "node server.js"
  },
  "dependencies": {
    "axios": "^1.6.0",
    "dotenv": "^16.0.3",
    "express": "^4.18.2"
  }
}

2. .env

ini
ETHERSCAN_API_KEY=your_etherscan_api_key

3. server.js

js
require('dotenv').config();
const express = require('express');
const axios = require('axios');
const path = require('path');
const app = express();
const PORT = process.env.PORT || 3000;

app.use(express.static('public'));

app.get('/check-wallet', async (req, res) => {
  const { address } = req.query;
  const apiKey = process.env.ETHERSCAN_API_KEY;

  if (!address) {
    return res.status(400).json({ error: 'Address is required' });
  }

  try {
    const balanceURL = `https://api.etherscan.io/api?module=account&action=balance&address=${address}&tag=latest&apikey=${apiKey}`;
    const txURL = `https://api.etherscan.io/api?module=account&action=txlist&address=${address}&startblock=0&endblock=99999999&sort=desc&apikey=${apiKey}`;

    const [balanceRes, txRes] = await Promise.all([
      axios.get(balanceURL),
      axios.get(txURL),
    ]);

    const balance = balanceRes.data.result;
    const transactions = txRes.data.result.slice(0, 5);

    res.json({
      balance: (parseInt(balance) / 1e18).toFixed(5),
      transactions,
    });
  } catch (err) {
    res.status(500).json({ error: 'Failed to fetch wallet data' });
  }
});

app.listen(PORT, () => {
  console.log(`Server running at http://localhost:${PORT}`);
});

4. public/index.html

html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
  <title>Crypto Wallet Checker</title>
  <style>
    body { font-family: Arial; margin: 40px; }
    input, button { padding: 10px; font-size: 16px; }
    #result { margin-top: 20px; }
  </style>
</head>
<body>
  <h1>Ethereum Wallet Checker</h1>
  <input type="text" id="walletAddress" placeholder="Enter Ethereum Address"/>
  <button onclick="checkWallet()">Check</button>

  <div id="result"></div>

  <script>
    async function checkWallet() {
      const address = document.getElementById('walletAddress').value;
      const resultDiv = document.getElementById('result');
      resultDiv.innerHTML = 'Loading...';

      try {
        const res = await fetch(`/check-wallet?address=${address}`);
        const data = await res.json();

        if (data.error) {
          resultDiv.innerHTML = `<p>Error: ${data.error}</p>`;
          return;
        }

        resultDiv.innerHTML = `
          <h3>Balance: ${data.balance} ETH</h3>
          <h4>Recent Transactions:</h4>
          <ul>
            ${data.transactions.map(tx => `
              <li>
                <strong>Hash:</strong> ${tx.hash.slice(0, 10)}... |
                <strong>Value:</strong> ${parseFloat(tx.value / 1e18).toFixed(5)} ETH |
                <strong>To:</strong> ${tx.to}
              </li>
            `).join('')}
          </ul>
        `;
      } catch (e) {
        resultDiv.innerHTML = `<p>Error fetching data</p>`;
      }
    }
  </script>
</body>
</html>

Run the App

bash
npm install
node server.js

Visit: http://localhost:3000

Optional Enhancements

  • Add QR code scanning for mobile wallets

  • Support multiple blockchains (e.g., BSC, Polygon, Bitcoin)

  • Add ENS name resolution (via web3.js or ethers.js)

  • Add wallet reputation (e.g., via Blockscan or Chainalysis APIs)

  • Deploy on Vercel, Netlify, or Heroku for public access

Let me know if you want a version using React, Python (Flask), or CLI-based version.

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