Where Does Google Find API Documentation?

The documentation of popular APIs is spread across many formats, from vendor-curated reference documentation to Stack Overflow threads. For developers, it is often not obvious from where a particular piece of information can be retrieved. To understand this documentation landscape, we systematically conducted Google searches for the elements of ten popular APIs. We found that their documentation is widely dispersed among many sources, that GitHub and Stack Overflow play a prominent role among the search results, and that most sources are quick to document new API functionalities. These findings inform API vendors about where developers find documentation about their products, they inform developers about places to look for documentation, and they enable researchers to further study the software documentation landscape.