In late 2005, Niall Kennedy blogged about Google Reader’s API: http://www.niallkennedy.com/blog/2005/12/google-reader-api.html
He mentioned that a couple of guys at Google suggested to him that the API might be made official within a couple of weeks.
Has the API ever been officially and publicly documented by Google?
No, despite the talk about Google doing this some day, there is no officially documented Google Reader API yet.
However, the API has been unofficially documented.
I've been successfully using https://github.com/brutuscat/googlereader that is a fork of http://code.google.com/p/pyrfeed/
If you want to see more samples, I wrote an article about how to use the lib to extract the main text content from an HTML. This is an alternative to boilerpipe mainly for blogs.
