> ## Documentation Index
> Fetch the complete documentation index at: https://docs.theblockchainlibrary.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Listen to Contract Events with ethers.js

> Subscribe to real-time smart contract events using ethers.js event listeners.

# Listen to Contract Events with ethers.js

Subscribe to real-time smart contract events using ethers.js event listeners.

Subscribe to real-time smart contract events using ethers.js event listeners.

## Explanation

Event listening lets you build real-time dashboards and notifications.

**Key points:**

* Use `WebSocketProvider` (not HTTP) for real-time streaming.
* `contract.on(eventName, callback)` fires on every matching event.
* Indexed parameters (`from`, `to`) are passed directly; non-indexed are in the last `event` object.

Remember to call `contract.removeAllListeners()` on cleanup to avoid memory leaks.

## Code

```javascript theme={null}
import { ethers } from "ethers";

const provider = new ethers.WebSocketProvider(
  "wss://eth-mainnet.g.alchemy.com/v2/YOUR_KEY"
);

const abi = [
  "event Transfer(address indexed from, address indexed to, uint256 value)"
];

const contract = new ethers.Contract(
  "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC
  abi,
  provider
);

contract.on("Transfer", (from, to, value, event) => {
  console.log(`Transfer: ${ethers.formatUnits(value, 6)} USDC`);
  console.log(`  From: ${from}`);
  console.log(`  To:   ${to}`);
  console.log(`  Tx:   ${event.log.transactionHash}\n`);
});
```

***

**Canonical knowledge ID:** `code-example:listen-contract-events-ethersjs`