[theOnliest]

(I also work at Fastmail, on the server side.)

It does describe APIs in general, and that is one of the reasons I like it so much. All of our internal APIs are JMAP: when you need to do something with a user, you call User/set; with a rule, call Rule/set, and so on.

JMAP makes it super easy to build new APIs because you can reuse most of the code; the only things you need to define are the data types (and any custom implementation for access controls, etc.).

Although Fastmail itself has much more legacy code (we’ve been around a while!), new things can start with a framework called Ix, which is available at https://github.com/fastmail/Ix. Ix is the basis for Topicbox (www.topicbox.com), which is built ground-up on top of JMAP.