Fix Vite "Port 5173 is Already in Use"

The error

When you run npm run dev or vite, you see:

Port 5173 is already in use.
  Use --port to specify a different port.

Vite defaults to port 5173. If an old Vite process, another dev server, or a background task is holding that port, Vite cannot start.

Fix 1: portrm (instant)

$ ptrm fix 5173
  Port 5173 in use
  node (PID 28091) - vite preview
  Killed PID 28091. Port 5173 is free.

$ npm run dev  # works now

Fix 2: Kill manually (macOS / Linux)

$ lsof -ti :5173 | xargs kill -9

On Windows:

> netstat -ano | findstr :5173
  TCP  0.0.0.0:5173  0.0.0.0:0  LISTENING  28091
> taskkill /PID 28091 /F

Fix 3: Change Vite's port

If you want to keep the other process running, configure Vite to use a different port:

// vite.config.ts
import { defineConfig } from 'vite'

export default defineConfig({
  server: {
    port: 3000,
    strictPort: true   // fail if 3000 is also taken
  }
})

Or as a CLI flag:

$ vite --port 3000

Fix 4: Auto-detect next available port

By default Vite already tries the next port, but only if strictPort is false (the default). If you have strictPort: true in your config, remove it or set it to false:

// vite.config.ts
export default defineConfig({
  server: {
    port: 5173,
    strictPort: false   // will try 5174, 5175, etc.
  }
})

Preventing Vite port conflicts