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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:

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.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

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