Gimp-Forum.net

So I've done some searching, but am unsure, whether there exists any API Reference for Script-Fu or Python-Fu.

If not, then would it perhaps be a good community project to undertake? Using something like Doxygen it shouldn't be too difficult.

For both, when you are in the script console (for instance FIlters>Python-fu>Console) you can hit the "browse" button to be taken to a dynamically-generated API reference. The advantage is that this includes any plug-ins you have as well(*).

(*) As a plugin author, the code you write to "register" the plugin includes this kind of documentation.