What’s running on port 3000 on my Mac?

Check what’s on port 3000

lsof -nP -iTCP:3000 -sTCP:LISTEN

A node command means Next.js, Create React App, Nuxt, Remix or an Express app. ruby means Rails (Puma). grafana or com.docker.backend means Grafana or some other container. To tell several Node projects apart, print the full command line and working folder:

ps -o pid,etime,command -p <PID>
lsof -a -p <PID> -d cwd -Fn | tail -1

Or with Stat Space installed:

statspace port 3000

Free it

If it’s a forgotten server, stop it with kill <PID>. Give it a few seconds to shut down; use kill -9 <PID> only if it ignores you. Docker containers need docker stop <name> instead, because killing com.docker.backend takes every container down with it. The full walkthrough is in how to kill a process on a port.

Or move your app

Tool	Change the port
Next.js	next dev -p 3001 or PORT=3001 npm run dev
Create React App	PORT=3001 npm start, or PORT=3001 in .env
Rails	bin/rails server -p 3001
Nuxt	nuxi dev --port 3001
Express	app.listen(process.env.PORT || 3001)
Grafana	http_port = 3001 under [server] in grafana.ini

Recent Next.js versions don’t fail when 3000 is taken: they quietly move to 3001. That keeps you working but hides the leftover server, so it pays to check what’s holding 3000.

Who can reach it

Look at the NAME column. 127.0.0.1:3000 is local only. *:3000 means every device on your network can open it. Next.js and Create React App bind to all interfaces by default, so on shared Wi-Fi your work-in-progress app and its API routes are reachable by others. Use next dev -H 127.0.0.1 or HOST=127.0.0.1 for CRA when you don’t need phone testing. More in dev server exposed to the network.

Seeing it live

Stat Space lists port 3000 with the framework it detected, the project folder, the launcher that started it (Terminal, VS Code, Cursor, Claude Code, Docker) and how long it’s been up. A *:3000 binding gets a warning, and stopping it asks first.