Like the author, I had the same problem when I was going through the GO tutorial as well (I have to say it's not the greatest tutorial for someone coming from a totally different programming background, I've never done C or Java for example). Interface in GO can be a little bit tricky to understand at first, but then they become kind of like a nice way of thinking about coding.

I can't help to think like what @tomp said. It's really up to the developers to annotate their code and document their Interfaces, specially when using a systems programming language like GO, comments are essential as the code is not as self-explanatory like Python or Ruby. GO provides an excellent tool to generate documentation from internal or external packages: http://golang.org/cmd/godoc/.

There's this great write-up on GO's Interface by Jordan Orelli: http://jordanorelli.tumblr.com/post/32665860244/how-to-use-i...