It took a long time to get right but the interface to the ActivityPub test suite is pretty nice. It's interactive only in the places that it needs to be, and you can "roll back" at any point if you submit the wrong information.

It's also using a pile of delimited continuations, GOOPS, and a state machine. I hurt my head doing it.

wraps some duct tape around the pieces for good measure, that'll hold it