127.0.0.1 — Localhost

127.0.0.1 is the loopback IP address, commonly known as localhost. It always refers to your own computer — any traffic sent to 127.0.0.1 never leaves your machine. Developers use it to test websites, APIs, and applications locally before deploying to production servers.

Access your local server: http://127.0.0.1
Same as: localhost | localhost:3000 | localhost:8080
Looking for your router? 127.0.0.1 is NOT a router IP. For router settings, try 192.168.1.1 or 192.168.0.1

What is 127.0.0.1?

The IP address 127.0.0.1 is a special reserved address that represents "this computer." When you type 127.0.0.1 in your browser or use it in code, you're connecting to a server running on your own machine.

Key Facts

  • 127.0.0.1 and localhost are identical
  • The entire 127.0.0.0/8 range (127.0.0.1 to 127.255.255.255) is reserved for loopback
  • Traffic to 127.0.0.1 never reaches the network — it stays on your computer
  • Every computer has 127.0.0.1 — it's defined by the operating system
  • IPv6 equivalent is ::1

127.0.0.1 vs localhost

127.0.0.1localhost
IP address (numeric)Hostname (text)
Always IPv4Can resolve to IPv4 or IPv6
No DNS lookup neededRequires hosts file lookup
http://127.0.0.1http://localhost

In most cases, they work identically. Use whichever you prefer.

Common Localhost Ports

AddressServiceUsed By
127.0.0.1:80HTTPApache, Nginx, XAMPP
127.0.0.1:443HTTPSSecure web servers
127.0.0.1:3000Dev ServerReact, Node.js, Rails
127.0.0.1:3306MySQLDatabase server
127.0.0.1:5432PostgreSQLDatabase server
127.0.0.1:5173ViteVue, React (Vite)
127.0.0.1:8080Alternative HTTPTomcat, Jenkins, proxies
127.0.0.1:8888MAMPMAMP default port
127.0.0.1:6379RedisCache server
127.0.0.1:27017MongoDBNoSQL database

Start a Local Server

Quick Options (No Install)

# Python 3
python -m http.server 8000
# Open http://127.0.0.1:8000

# Python 2
python -m SimpleHTTPServer 8000

# PHP
php -S localhost:8000

# Node.js (npx)
npx serve

Development Stacks

  • XAMPP — Apache + MySQL + PHP (Windows/Mac/Linux)
  • MAMP — Apache + MySQL + PHP (Mac)
  • WAMP — Apache + MySQL + PHP (Windows)
  • Laragon — Modern stack (Windows)

Hosts File

The localhost hostname is defined in your computer's hosts file:

OSHosts File Location
WindowsC:\Windows\System32\drivers\etc\hosts
Mac/Linux/etc/hosts

Default entry: 127.0.0.1 localhost

Why Use Localhost?

  • Development — Test websites before going live
  • Speed — No network latency, instant responses
  • Security — Code never leaves your computer
  • Offline — Works without internet connection
  • Cost — No hosting fees during development

Troubleshooting

"Connection Refused" Error

No server is running on that port. Solutions:

  • Start your web server (Apache, Nginx, Node, etc.)
  • Check if you're using the correct port
  • Verify the service is actually running

"Address Already in Use"

Another application is using the port:

# Find what's using port 3000
# Mac/Linux
lsof -i :3000

# Windows
netstat -ano | findstr :3000

Test if Localhost is Working

# Ping test (should always work)
ping 127.0.0.1

# Check if port is open
# Mac/Linux
nc -zv 127.0.0.1 80

# Windows PowerShell
Test-NetConnection -ComputerName 127.0.0.1 -Port 80