tl;dr: it's a tool to link people to markdown files in https://github.com/expo/fyi with a concise and pretty link. For example, https://expo.fyi/bundle-identifier

This website is a useful URL shortener that redirects users to a markdown file on the https://github.com/expo/fyi repository. For example, https://expo.fyi/bundle-identifier will redirect the user to https://github.com/expo/fyi/blob/master/bundle-identifier.md.

It is useful to remove any friction to create a shareable link to a persistent explanation of some piece of knowledge that is useful to developers using Expo tools.

Imagine that you're working on Expo CLI and want to add more context on some terminology that you are using in a prompt to the user. Maybe you need to ask them for a "bundle identifier". You want to make sure that the user has easy access to more information about what that means, but you don't want to inline a whole explanation of it and crowd the interface. At the same time, you can't be bothered to create a docs page for this, or maybe the existing docs page doesn't provide the most relevant context for the situation the user is in. That's understandable. So instead let's just create an FYI!

• Go to https://github.com/expo/fyi.
• Click "Create a new file".
• Pick a name for it and include the .md extension. If you are teaching people about the "tunnel" connection type in expo-cli, maybe you want to call it tunnel-connection.md and then the URL will be https://expo.fyi/tunnel-connection.

• You can add any arbitrary string like this-does-not-exist to the URL and it will just bring you to the GitHub 404 pages: https://expo.fyi/this-does-not-exist. You probably do not want to do this, so instead create a file and link to it, and don't delete the file if it's linked to from somewhere already.
• If you go to https://expo.fyi it will just redirect you to the GitHub repo.
• You can create your own domain like this by cloning https://github.com/expo/expo-fyi — a small service that you can deploy to, for example, Vercel or Netlify. Customize the URLs it uses in index.js.