A JSON file describing how your site should behave if someone installs it to their home screen as a web app — its name, icon, colours and display mode.
Powers the 'Add to home screen' / installable-app experience on mobile and desktop browsers, and is a baseline requirement for a Progressive Web App.
A genuine W3C Web App Manifest standard.
Site root: example.com/manifest.json, linked from your HTML with
Fill this in and download manifest.json directly — the same generator lives in the full builder alongside the other 15 files.