How to Check If a Port Is in Use on Mac

You start a dev server and get EADDRINUSE: address already in use. Something is already listening on that port. Here is how to find it and free the port in under a minute.

Run lsof on the port

Open Terminal and run this, replacing 3000 with your port:

lsof -nP -iTCP:3000 -sTCP:LISTEN

lsof lists open files, and on Unix a network socket counts as a file. The flags mean: -n and -P skip slow hostname and port-name lookups, -iTCP:3000 limits results to TCP on port 3000, and -sTCP:LISTEN shows only processes actually listening.

If nothing prints, the port is free.

Read the output

A hit looks like this:

COMMAND   PID  USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    48213 sam     23u  IPv6 0x1a2b3c      0t0  TCP *:3000 (LISTEN)

The two columns you care about are COMMAND (what it is) and PID (the process ID you will use to stop it).

Stop the process

Send it a normal termination signal using the PID from the previous step:

kill 48213

Most processes exit cleanly. If it is still there after a few seconds, force it:

kill -9 48213

Use -9 only as a fallback. It skips the process's cleanup, which can leave temp files or lock files behind.

Confirm the port is free

Run the first command again:

lsof -nP -iTCP:3000 -sTCP:LISTEN

No output means the port is yours. Start your server.

One-liner for next time. If you do this often, this finds and kills whatever is on the port in one step:

kill $(lsof -t -iTCP:3000 -sTCP:LISTEN)

-t prints only PIDs, which kill then receives. It errors harmlessly if the port is already free.