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.