How do I kill the process on port 3000?

On Mac/Linux, run 'npx kill-port 3000' or 'lsof -i :3000' followed by 'kill -9 '. On Windows, use 'netstat -ano | findstr :3000' and then 'taskkill /PID /F'.

Why does localhost 3000 say connection refused?

This usually means your web server (React, Node, etc.) is not running, or it crashed. Check your terminal for errors and ensure you ran 'npm start' or 'npm run dev'.

Localhost 3000 Not Working? Ultimate Fix Guide & Port Analysis

Fixing "Localhost Refused to Connect" Errors

If the link above didn't work, your development server is likely offline or facing a port conflict. Here is the developer's guide to fixing it.

Common Error

1. Check if the Server is Running

The most common reason for ERR_CONNECTION_REFUSED is that the server process isn't active. Open your terminal/VS Code and ensure you have run the start command:

# For React / Next.js
npm run dev

# For Node / Express
npm start

Port Conflict

2. Fix "Port 3000 Already in Use"

If you see an error saying the address is in use (EADDRINUSE), a previous process didn't close correctly. Use these commands to force kill it.

MacOS / Linux:

# Find and kill the process automatically (Requires npx)
npx kill-port 3000

# OR manual method
lsof -i :3000
kill -9 [PID]

Windows (CMD/PowerShell):

# Find the Process ID (PID)
netstat -ano | findstr :3000

# Kill the process (Replace 1234 with your PID)
taskkill /PID 1234 /F

3. HTTPS vs HTTP Mismatch

Sometimes Chrome enforces HTTPS on localhost. Ensure you are visiting http://localhost:3000 and not https://.... You can test this by trying to open the link in Incognito mode.

What is Localhost 3000?

Localhost refers to your computer's internal IP address (Loopback address 127.0.0.1). Port 3000 is the default communication channel used by many modern JavaScript frameworks during development.

Why 3000?

It is the default configuration for:

React (Create React App)
Next.js
Node.js (Express default examples)
Ruby on Rails (Puma server)

How to Change the Default Port?

If port 3000 is busy, you can change it in your package.json scripts:

"scripts": {
  "start": "PORT=4000 react-scripts start"
}

For Windows users (without cross-env):

"scripts": {
  "start": "set PORT=4000 && react-scripts start"
}