What is a Web App Manifest?

We use “web app” to describe web pages which are more like programs. This has always been pretty informal and ambiguous (take a slideshow in a news story; is it a web app or a web page?). The “Web App Manifest” attempts to formalize the distinction, and says that a “web app” is any web page with a <link rel="manifest" href="/manifest.json"/>, where /manifest.json is a JSON file with a bunch of information about the web app, for example:

{
  "name": "jameshfisher.com",
  "start_url": "/",
  "icons": [
    {
      "src": "/assets/jim_144.png",
      "sizes": "144x144",
      "type": "image/png"
    }
  ],
  "display": "standalone",
  "gcm_sender_id": "432193615425"
}

The manifest gives the web app things which make it more like “real applications”, like:

Ability to be added to a “homescreen”
Icons for launching
Configuration for advanced features, like web push
Links to other applications in other “app stores”

It’s not clear to me why all this stuff has to go in a separate JSON file. It could all go directly in the <meta> tags for the page. We already have a million different <meta> tags for other things.

In Chrome, you can see the contents of the manifest in Developer Tools under Application > Manifest. On thing you can do here is “Add to homescreen”. Now this blog can be on your homescreen, which I’m sure you’ve all been waiting for.

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What is a Web App Manifest?

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