Every local dev server listens on a port: React and Next.js on localhost:3000, Vite on 5173, Angular on 4200, Jupyter on 8888. Pick a port to see what runs there, how to fix it and how to share it.
Basics
Web frameworks
- localhost:3000React, Next.js, Nuxt, Rails, Express and Grafana.
- localhost:5173Vite dev server (React, Vue, Svelte, SvelteKit).
- localhost:4200Angular CLI dev server (ng serve).
- localhost:8000Django, python -m http.server, Laravel, FastAPI/uvicorn, Gatsby.
- localhost:5000Flask, ASP.NET Core (Kestrel fallback), Docker Registry, macOS AirPlay.
- localhost:3001Second dev server, API next to a frontend, BrowserSync UI, Uptime Kuma.
- localhost:8080Tomcat, Jenkins, Spring Boot, Vue CLI and many Docker images.
- localhost:8081React Native Metro, Expo, Nexus Repository, second HTTP server.
- localhost:9000PHP-FPM, SonarQube, MinIO API, Portainer (legacy), ClickHouse.
Data, AI and automation
What each page covers
Each page says what usually runs on that port, how to start it, how to find and free the port when something else is holding it, and how to open it from another device. The last section covers sharing it with anyone on the internet over an HTTPS URL.
localhost always means this machine: it resolves to the loopback address 127.0.0.1 (or ::1 on IPv6), and nothing outside your computer can reach it until you forward or tunnel the port.