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

What it means

Another copy of your app (or another program) is already using the same 'door' (port) on your computer, so the new one can't open it.

How to fix it: paste this prompt into your AI builder

My dev server fails with EADDRINUSE. Don't change app code. Tell me the exact command to find and stop the process using that port on my OS, and optionally make the dev server port configurable via a PORT env var.

If the AI can't fix it: manual steps

1. Close other terminals running npm run dev, or restart your computer.
2. Mac/Linux: run 'npx kill-port 3000' (replace with your port).

Where this happens

Seen in these AI app builders and editors:

Sources

• https://stackoverflow.com/questions/4075287/node-express-eaddrinuse-address-already-in-use-kill-server

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• Node.js version mismatch (Unsupported engine / requires Node >= 18)#56 · dependencies
• npm ERR! enoent Could not read package.json#57 · dependencies