Port Collision Radar – macOS menubar app that watches your listening TCP ports

Francesco — Sat, 21 Feb 2026 16:08:56 +0000

I built a radar for your ports

Every developer has been there. You run npm start and get hit with:

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

You sigh. You run lsof -i :3000. You kill the rogue process. You move on with your life — until it happens again tomorrow.

I got tired of this. So I built Port Collision Radar, a macOS menubar app that watches your listening TCP ports in real-time and tells you the moment something takes over a port it shouldn't.

What it actually does

The app sits in your menubar and scans lsof every 4 seconds. It tracks which process owns which port. When ownership changes — say, a zombie Node process grabs port 3000 before your dev server can — it flags it as a collision.

There are two views:

Radar view — a circular visualization where ports appear as color-coded dots. Inner ring is well-known ports (0–1023), middle ring is registered ports (1024–49151), outer ring is ephemeral. The dots are colored by process, so you can instantly see clustering.
List view — a searchable table with port numbers, process names, PIDs, and status.

Collisions pulse red. New ports glow yellow. Everything else is calm cyan.

Why a radar?

Because staring at netstat output is miserable. I wanted something I could glance at in my menubar and immediately know if something was wrong. The radar metaphor clicked — ports are "out there" on your system, and you're scanning for them.

It's also just... fun? There's something satisfying about watching your ports orbit on a little radar while you work.

The stack

It's dead simple:

Electron + menubar npm package for the macOS menubar integration
Vanilla JS — no React, no framework, no build tools
Canvas API for the radar animation
lsof for port scanning (the same tool you'd use in the terminal)
electron-builder for packaging as a signed + notarized universal dmg

The entire app is ~600 lines of code across 6 files.

Try it

brew tap fran-mora/homebrew-tap
brew install --cask port-collision-radar

Or grab the .dmg from GitHub Releases.

The source is open: github.com/fran-mora/port-collision-radar

What's next

A few ideas I'm considering for v2:

Docker container port mapping awareness
Network-wide scanning (not just localhost)
Historical port usage timeline
Notifications when specific ports get claimed

If any of those sound useful, let me know — or open an issue.

Built with frustration and Electron by Francesco Moramarco.