tl;dr: it's a tool to link people to markdown files in https://github.com/expo/fyi with a concise and pretty link, eg: 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 creating 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 a 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 would call it tunnel-connection.md and then the url would 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 now.sh. Customize the URLs it uses in index.js.