Owl serves a JSON-RPC 2.0 API as a means of communicating with a running instance. This is the preferred way of using Owl since applications can be notified of incoming messages as they happen.
There is a Go client available for this API.
If you are using another lanaguage you can get an idea for what the API produces by looking at the interfaces here.
The names of the JSON fields are annotated on the structs in Go.