(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

(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 https://github.com/fastmail/Ix. Ix is the basis for Topicbox (www.topicbox.com), which is built ground-up on top of JMAP.