Have you seen Optic (https://www.useoptic.com)? It’s a git-like tool for capturing API documentation.

a former colleague started another startup here, Akita, so I've been thinking a bit about these. I like this idea as a developer for when a third-party API stinks, but as an API provider, this a painfully indirect approach. I want to document our APIs and generate good UIs for that, and less interested in reverse engineering & comparing, which these focus on, and I assume, are thus less focused on doing a good job when we can give that data.