Documenting your API within your repo
Normally your go-to solution to document and test your API would be Postman which is great tool.
But recently I came upon this VSCode extension that does a similar job and I don't have to leave my editor. Plus I can just check it in my git repo. While it's possible to export the Postman data into a file and do the same this feels much more part of your project.
It's simple, you can define variables and different environments, it works for REST as well as GraphQL APIs.
Just have a look at the documentation to learn how to use it.