How to Free Port 3000 on Mac

Dev servers for Node, Express, Create React App, Next.js and Rails commonly default to port 3000. If a previous run didn’t shut down, you get:

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

Fix it in Terminal

lsof -nP -iTCP:3000 -sTCP:LISTEN     # find the PID
kill <PID>                            # polite stop

Or in one step:

kill $(lsof -ti tcp:3000 -sTCP:LISTEN)

Still running? kill -9 <PID> as a last resort. Confirm with the first command again.

Why it happens

• A previous npm start was suspended (Ctrl+Z) instead of stopped.
• A terminal tab closed but the child process lived on.
• Another project’s server is on 3000.

Don’t want to kill it?

Run on another port: PORT=3001 npm start (varies by framework, e.g. next dev -p 3001).

Without Terminal

Open PortPeek from the menu bar, type 3000, and click Kill Process. You see which app owns the port first, and PortPeek confirms the port is free afterwards.