I'm a developer and I love connecting data. I know this is a planned feature for Roll20, but i want to throw some ideas of what I think would be helpful as to both Roll20 and 3rd party applications that might interact with it. I would expect two versions of the API to exist: Inbound and Outbound. Inbound would be responsible for new data or editing existing data while Outbound would primarily be event driven.
Inbound API
The inbound API would give the application the ability to create charactors, handouts, ect from external sources. Rather than copy pasting everything in we can click a button.
Expected Methods:
Charactors
Handouts
Chapters
Current Chapter
Chat
Outbound API
The outbound API would work on hooks which could be configured with an interface or via API methods. Primarily I expect chat methods to be the most useful. Send an API call saying when command "/{x}" is sent in chat, send that to the predefined system.