File Existence

Looks for a web manifest file declared in the HTML and checks to make sure it exists.

A web manifest file is a JSON file that can be used by web browser to discover certain information about the website. It is useful for making Progressive Web Apps that can be installed on the homepage of a user's mobile device, as well as for other purposes. A proper web manifest file allows users to create shortcuts to the website which have an optimized name and icon. Here is an example of a minimum web manifest:

{
"name": "ValidBot - Website Testing",
"short_name": "ValidBot",
"icons": [ {
     "src": "/android-chrome-192x192.png",
     "sizes": "192x192",
     "type": "image/png"
   }, {
     "src": "/android-chrome-512x512.png",
     "sizes": "512x512",
     "type": "image/png"
   } ]
}

For more information, please read the documentation on MDN Web Docs.