Find what is using a port

lsof lists the program listening on a port: lsof -iTCP:3000 -sTCP:LISTEN names the process and its ID, so you can see whether it is an old server you forgot to stop.

How

What is listening on port 3000:

lsof -iTCP:3000 -sTCP:LISTEN -P

Every port something is listening on:

lsof -iTCP -sTCP:LISTEN -P

Or just ask Titan

Something is using port 3000 — find it and tell me what it is. Do it with Titan

Titan is an AI that lives on your computer: tell it what you need and it does it while you watch — you press Return, nothing runs by itself. What is Titan?

Titan isn’t on this computer yet. Get Titan, then press the button again — the task will be waiting, typed in.

Related

Free up a port that is in use Find what is slowing your computer down