We Built a Chrome Extension for Developers: Localhost App Detector
If you’ve ever had to mentally track which dev server is running on which port — or wasted time opening tabs trying localhost:3000, localhost:3001, localhost:8080 one by one — this is for you.
We built and published Localhost App Detector, a free Chrome extension that automatically detects all your running local development servers, scans ports intelligently, and lets you save and organize your configurations. No more guessing.
The Problem It Solves
Modern web development is multi-service by default. A typical day might have you running a React frontend on 5173, a Node API on 3000, a Python FastAPI service on 8000, a Redis instance on 6379, and a local docs server on 8080 — simultaneously.
Your options for keeping track of all this were:
- Remember it all. Works great until you take a long weekend.
- Check a notes file. Classic. But it’s never updated.
- Scan ports manually.
curl localhost:3000,curl localhost:3001… tedious. - Hope your terminal tabs are still labeled. They aren’t.
Localhost App Detector fixes this at the browser level, where you’re already working.
What It Does
Automatic Detection
The moment you visit any localhost or 127.0.0.1 URL in Chrome, the extension logs it. Click the toolbar icon and you’ll see every port you’ve accessed, complete with last-seen timestamps. Apps that have been idle for 5 minutes auto-expire to keep the list clean.
One click on any detected app opens it in a new tab.
Intelligent Port Scanner
The real power feature is the scanner. Hit “Quick Scan” and it probes ~100 common development ports in 3–5 seconds. “Deep Scan” covers 400+ ports across all categories including databases, message queues, and monitoring tools.
The scanner doesn’t just report open ports — it identifies what’s running on them. It recognizes 40+ server types from HTTP response headers:
| Category | Detected Servers |
|---|---|
| Web Servers | nginx, Apache, Caddy, Traefik, HAProxy, IIS |
| Node.js | Express, Fastify, Hapi, Koa |
| Python | Uvicorn, Gunicorn, Werkzeug, FastAPI, Django |
| Ruby | Puma, Unicorn, WEBrick |
| Java | Tomcat, Jetty, Undertow, WildFly |
| Go | Gin, Fiber, Echo |
| Rust | Actix, Rocket, Axum |
| .NET | Kestrel |
Each result shows the server type, HTTP status, content type, response time in milliseconds, and detected framework. It even correctly identifies macOS Control Center on port 5000 so you don’t chase phantom “servers.”
Saved Apps Manager
Detected apps are ephemeral by default. The Saved Apps tab is for the servers you use repeatedly. Pin any app to save it, then add:
- Custom names — “Main API”, “Auth Service”, “Storybook”
- Tags — group by project or tech stack
- Notes — document environment variables, startup commands, or quirks
- Favorites — star the ones you reach for constantly
Saved apps persist across browser sessions via Chrome’s sync storage, so they follow you to other machines. Import/export as JSON makes team sharing straightforward.
Custom Hosts Management
Working with a local staging environment mapped to app.local or api.dev? The Custom Hosts tab lets you configure hostname mappings similar to /etc/hosts, with a paste-from-hosts-file import and a generate-for-sharing export.
Privacy First
Developer tools that phone home are a liability. This one doesn’t.
The extension only ever touches localhost and 127.0.0.1 traffic. It requests the minimum viable Chrome permissions — tabs, webRequest, and storage — and uses none of them to contact external servers. Everything stays in your browser.
No analytics. No telemetry. No accounts. No data collection.
The full privacy policy is at gtmenterprisesllc.com/extensions/localhost-app-detector/privacy-policy/.
Built on Manifest V3
The extension runs on Chrome’s current Manifest V3 architecture, using a service worker for background port monitoring rather than the legacy persistent background pages. This means lower memory usage and better alignment with Chrome’s security model going forward.
Install It
Get Localhost App Detector on the Chrome Web Store →
It’s free. No account required.
If you want to dig into the source code, customize the port list, or add detection for a server type we missed, the repository is on GitHub at github.com/GTM-Enterprises-LLC/chrome-extension-localhost-helper. Contributions welcome.
What We’re Thinking About Next
A few things on the roadmap:
- Firefox support — the core functionality is largely portable
- Keyboard shortcuts — power-user access without clicking the icon
- Project groupings — associate a set of saved apps with a project so you can switch contexts cleanly
If any of those sound useful, or you have a feature request, open an issue on GitHub or reach out directly.
Building tools that make developers’ day-to-day less frustrating is something we enjoy. If your team needs custom internal tooling, developer portals, or workflow automation, let’s talk.
