  A good documentation is essential for a good usability of (security) APIs,
i.e. especially for the correct use of the APIs. Requirements for good
documentation of APIs have been described in several papers, but there is no
technical implementation (hereinafter referred to as a documentation system)
that implements these requirements. The requirements can be divided into
requirements for the documentation system and requirements for the
documentation content. Out of 13 identified requirements for a documentation
system itself, 9 were implemented in a prototype and evaluated in a user study
with 22 test persons using a cryptographic API. It turned out that the
implementation of the requirement 'Enable quick use of the API' depends on the
one hand on the quality of the content entered, but on the other hand also
includes 5 other requirements or their implementation. The two other
implemented requirements ('classic reference' and 'question and answer
function') were hardly or not at all used by the test persons. Their usefulness
and relevance should be investigated in a long-term study.
