Why won’t localhost:3000 open on another computer?

What does the 3000 mean?

It is the port where your application receives connections. Development tools often use 3000; others use 4321, 5173, or a different number. The number identifies an entry point on that computer. It does not publish the application on the internet. The addresses 127.0.0.1 and [::1] also point back to the local computer.

How to show someone your application

Choose based on where the person is and what they need to do. Use test data for a demonstration.

On a local network, an address might look like http://192.168.1.42:3000. This is only an example: use the actual IP of the computer running the application. Accepting network connections can give others on that network access; keep the test limited to trusted devices and test data. Do not disable the firewall or open router ports to the internet to solve a demo problem.

If it still will not open

• Check that the application is still running and the address uses the correct port.
• If you use a local IP address, confirm both devices are on a network that allows them to communicate and that the server accepts network connections.
• If the page loads but its data fails, check whether the browser is still calling an API at localhost. That request also goes to the visitor’s computer. The API needs a reachable address and the appropriate access permissions.
• If you use a hosted preview, check the link permissions and the configuration of connected services. Keep passwords and private keys out of code delivered to the browser.

When the team starts depending on it

Opening the application is the first step. If it will hold real work, you also need to check who can see and change each piece of information, how data can be recovered, and what happens when an operation fails. Tests should cover the workflow people will actually use.

The prototype shows what the application can do. A production readiness review establishes what still needs attention before people depend on it every day.