Port 3000 already in use on Mac: find what’s using it and stop it

You run npm run dev and get one of these:

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

⚠ Port 3000 is in use, trying 3001 instead.

Something on your Mac is already listening on port 3000. Usually it’s a dev server you started earlier and forgot about: in another terminal tab, in a closed editor window, or started by a coding agent. Here’s how to find it and stop it.

The short answer

# See what's listening on port 3000
lsof -nP -iTCP:3000 -sTCP:LISTEN

# Stop it (replace 12345 with the PID from the output)
kill 12345

If you just want port 3000 back and don’t care what it was:

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

Find the process using the port

lsof (“list open files”) ships with macOS and treats network sockets as files:

lsof -nP -iTCP:3000 -sTCP:LISTEN

COMMAND   PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    48213  tom   23u  IPv6  0x1c2…      0t0  TCP *:3000 (LISTEN)

What the flags do:

• -iTCP:3000 only shows TCP sockets on port 3000.
• -sTCP:LISTEN only shows sockets that are listening, not connections your browser has open to the server.
• -n and -P skip DNS and port-name lookups, so it answers instantly and shows 3000, not hbci.

If nothing prints, nothing on your Mac is listening on that port. If a process owned by another user holds it, run the same command with sudo.

Work out what it actually is

node and PID 48213 rarely tell you which project it is. Two more commands do:

# The full command line
ps -ww -o command= -p 48213

# The folder it was started in
lsof -a -p 48213 -d cwd -Fn | tail -1 | cut -c2-

Now you know it’s, say, next dev in ~/code/marketing-site, and you can decide whether you still need it.

Stop it

kill 48213

kill sends SIGTERM, which asks the process to shut down cleanly. Give it a second. If it’s still there, force it:

kill -9 48213

-9 (SIGKILL) can’t be ignored, but the process gets no chance to clean up, so try the polite version first.

Why the port sometimes comes straight back

Many dev tools run the real server as a child of a watcher: npm run dev starts next dev, which starts a worker; nodemon restarts your app when it exits. Kill only the process holding the socket and the parent may start a new one, or exit and leave other children behind.

Find the parent and stop that instead:

ps -o ppid=,command= -p 48213

Or stop the whole process group in one go:

kill -- -$(ps -o pgid= -p 48213 | tr -d ' ')

One-off tools

If you do this often, a couple of npm tools save typing:

• npx kill-port 3000 stops whatever is on port 3000.
• npx fkill-cli gives you an interactive, searchable process list.

Both answer “what’s on this one port, kill it”. They don’t tell you which project the server belongs to, or warn you before the next one piles up.

Stop it happening again

The error is a symptom. The cause is that dev servers are invisible once their terminal is out of sight, so they accumulate. A few habits help:

• Close servers from where you started them. Ctrl+C in the terminal lets the tool shut down its whole process tree.
• Give each project its own port. Put it in the dev script, such as next dev -p 3100 in one project’s package.json and vite --port 3200 in another’s, so two projects never fight over 3000.
• Make port conflicts loud. Vite’s --strictPort exits instead of quietly moving to 5174. See why Vite jumps to 5174 and Next.js to 3001.
• Keep every server in view. That’s what WhatThePort does.

With WhatThePort

WhatThePort lives in your Mac’s menu bar and lists every dev server that’s running, by port, project name and git branch, with memory and CPU for its whole process tree. Press ⌥⌘P, find :3000, and you can see it’s marketing-site on main, up for two days. Hover the row and click stop: WhatThePort sends SIGTERM to every process in the tree, then SIGKILL if anything is still running a few seconds later.

It’s free and open source. Download WhatThePort for Apple Silicon Macs on macOS 14 or later.