Localhost
Your own computer acting as a web server, so you can open the app in a browser before it's deployed.
What it is
Localhost means "this computer." When you run a dev server (often npm run dev), it starts a private copy of the app that only you can see, at an address like http://localhost:3000. The number is the port, like a door number on your machine.
The dev server usually reloads the page as code changes, so it's where you try things out. It keeps running in its terminal tab until you stop it with Ctrl + C, and if you close that tab, the page stops loading.
A localhost link only works on your own computer. Sending it to a teammate won't work; they need a deployed or preview URL.
How to ask for it
“I sent my coworker the link and it doesn't open for them.”
“My app runs at localhost:5173 on my machine. Give me a preview URL my coworker can open, and tell me whether it'll keep working after I close my laptop.”
Recognizing the link is localhost explains why it fails for others and asks for the right thing: a shareable preview.
You've seen this in
- L"Local: http://localhost:5173" printed by Vite
- AA browser tab pointed at localhost:3000
- U"Port 3000 is already in use" errors