or the code.

depending on this API, it could just be easier to look at the code. Seriously, if it is just exposing some database tables, then I don't necessarily always see the point of extra documentation. With extra docs you have to answer:

    * Who writes the docs?
    * Who reads the docs?
    * Where are the docs?
    * When are the docs written?
    * How are the docs written?

Basically, unless you have a dead-simple process, or a docs champion, you've just created another project. If you can answer these questions:

    * Who writes the codez?
    * Who reads the codez?
    * Where are the codez?
    * When are the codez written?
    * How are the codez written?

Then the simplest thing may be "just read the code"