There's also openapi [1], but there's a real social/process challenge in keeping it in sync with the actual implementation. The tools that build on it are great, but there's a lot of surface area to cover when bolting on computer-understanding to an existing api.

GraphQL's approach of mandating introspection means more work in some areas, and far less in others. Searching for the data available in a REST api can be a big issue, for example, depending on the state of the documentation.