Localhost

Localhost is the name your computer uses to reach a project running on that same computer, so only you can open it until you deploy the project somewhere public.

Localhost is the name your computer uses to reach a project running on that same computer, so only you can open it until you deploy the project somewhere public. When you start a to-do app on your own machine, the assistant typically prints an address like http://localhost:3000, and that address loops straight back to your computer instead of traveling across the internet. You can open it in your browser and click through every screen, but a teammate on another machine cannot reach that same link, because localhost always points to wherever the browser is sitting. Going from this private preview to a shared web address is the job of deployment.

Builder example

Running on localhost lets you preview and test a project before anyone else sees it, which keeps half-finished work and broken screens off the public web. When you ask an AI assistant to build a feature, it usually runs the project locally first so you can confirm the password reset flow or the new form behaves before you spend any time deploying. Treat the localhost link as your private rehearsal space, then deploy once the behavior is right.

Common confusion: Seeing your project work on localhost means it runs on your computer. It does not mean anyone else can reach it. The localhost address resolves only on the machine that opens it, so you have to deploy the project to a server before a visitor can load it.