We have just published our guidelines for designing REST APIs.
Some of our applications already have REST APIs but so far they have been developed in an ad hoc way without too much attention to how other applications implement theirs. The goal of the guidelines is to get more consistent APIs across Atlassian applications so that as a user of those APIs you know what to expect and how to interact with them.
We wanted to make this document public for two main reasons. The first one being that we value community feedback and while we worked at making those guidelines the best possible they can get better through your feedback. The second reason is that applications will soon provide a new extension point allowing plugin developers to write their own RESTful API for our products. This will be based on JAX-RS 1.0. We wanted the plugin developers to benefit from our work and allow them to make their APIs consistent with Atlassian written ones.
Enough talking. Go read the guidelines and don’t hesitate to provide your feedback.