https://www.google.com/reader/api/0/stream/contents/feed/FEEDHERE?output=json&n=20
I'm using this right now to parse RSS and Atom feeds, for a lot of reasons. But there is no official API key or something so I'm afraid something may break in the future, like Google stopping my access if I make a lot of queries.
Is there an alternative to this with API keys?
Try Google Feed Api, it is easy to use. It supports JSON and XML formats, but it is limited to a maximum of 250 feeds per url.