# `Error: listen EADDRINUSE: address already in use :::3000`

**Where it appears:** Terminal

**What it means:** Another program is already using port 3000, so your app can't start there.

## Likely causes

- An old copy of your app is still running in another terminal.
- Another app on your computer uses port 3000.

## Message for your agent

```text
Find what's using port 3000, tell me what it is, and stop it if it's an old copy of my app.
```

**Prevention:** Stop the app (Ctrl + C) when you finish.

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Source: [Agentic Makers](https://agenticmakers.app/en/help/errors/eaddrinuse-address-already-in-use) · License: CC BY 4.0