Build a Multi-Chain Crypto Wallet Monitor in Node.js (15 minutes)

#crypto #javascript #node #tutorial

Want to watch your crypto wallets across Ethereum, Base, Polygon, Arbitrum, and Optimism without signing up for anything? Here's the shortest path.

The one dependency

npm install wallet-watcher

const { getBalances } = require("wallet-watcher");
const balances = await getBalances("0xYourWallet");
// { eth: {symbol:"ETH", balance: 1.23}, base: {...}, polygon: {...}, ... }

No Alchemy key, no Infura signup, no web3 SDK. Public RPCs, one call,
five chains (BTC addresses work too).

Turn it into a monitor

Wrap it in a loop, diff the result, and you have a watcher:

setInterval(async () => {
  const now = await getBalances(WALLET);
  for (const [chain, info] of Object.entries(now)) {
    if (prev[chain] && prev[chain].balance !== info.balance)
      console.log(`🔔 ${chain}: ${prev[chain].balance} → ${info.balance}`);
  }
  prev = now;
}, 5 * 60 * 1000);

Turn it into a trading-bot base

I open-sourced a starter template that wires this into a clean loop with a
strategy file you own: crypto-bot-starter.
Edit strategy.js, plug in Telegram alerts, done.

When you actually need to swap

If you're moving between tokens, swapdeck.net is a
minimal no-signup swap UI for the same chains — connect and swap, no account.

Why this stack

Most tutorials start with "create an Alchemy account." For read-only balance monitoring, public RPCs are plenty — fewer keys in your .env, fewer things that can leak, faster setup. Keep the private keys for what actually needs them.

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