one criticism of activitypub is that it's not a specification, and as a consequence you have to test extensively to ensure interoperability between implementations.

this is a valid criticism.

  1. minimally you need to implement a few things beyond activitypub to get even basic interoperability with popular implementations—http signatures at a minimum (and a draft version of that) and probably webfinger. (i guess this really isn't a problem with activitypub per se, but it sure feels like it is.)
  2. the recommendation doesn't tell you what to do with the various object types, so even if you get the basic transport working, you don't really have an application. what's the right way to implement an interoperable "comment", for example?
  3. and then there are interoperability problems in practice—just scan the issues for popular implementations. these have to be identified and fixed multiple times, every time someone spins up a new implementation.

to some degree i guess i don't care. i'm building a free/open source application not a commercial product, and it's aimed at relatively tech-savvy users, and i kind of enjoy spelunking issues like these anyway, but for anyone whose goal is mass adoption of the "fediverse" concept, it's a problem.

#activitypub #ktistec