package.json
The Quick Version
Your project's ID card and shopping list.
How it actually works
It records your project's name, its scripts (dev, build, preview) and every dependency with a version range. Package managers read it to reproduce your setup on any machine.
Why does it matter?
Hosting platforms read your scripts from here to know how to build and start your app.
Example
"scripts": { "build": "vite build" }