Developers use localhost : 3000 to see the preview of the developed application and test it according to the requirements for responsiveness and other parameters before deploying it to production. Localhost:3000 is the most popular development server port , widely adopted across multiple frameworks and platforms. “Localhost” refers to your own computer (typically mapped to IP address 127.0.0.1), and “3000” is the port number where development servers listen for connections. Given that the port is bind to any IP address other than 127.0.0.1 ( localhost ), you can access it from any other system. To view your IP addresses, use ipconfig (Windows) or ifconfig (Linux) command. Find out the IP which is in the same network as the "other system" from which you want access. Then access it like, for example: 172.16.0.12: 3000 . PS: Remember to include the port 3000 even when accessing it through another system. Also, hostnames may be used in place of IP addresses, if configured. This will start the React app on port 3001 instead of the default port 3000 . Using Environment Variables Alternatively, you can create a .env file in the root of your React project and add the line PORT=3001. This permanently sets the environment variable for your project; every time you run the npm start command, the app will listen on the specified port. What is running on localhost 3000 ? Identifying Localhost Services When something runs on localhost 3000 , it's typically a development ...
