OpenAPI is a specification that defines the interface to an API. With one, you can generate client code and documentation for an API. The spec file is usually generated by the server.
My request is for OGS to create and release an OpenAPI spec for the server. I understand that the server cannot be open-sourced right now, but this would go a long way toward making the API easier to use.
I suppose my real request is for comprehensive documentation and accompanying client libraries. I think the community could create those if we had formatted API info to work with 
This is a fairly minor request, since it’s still possible to figure out any API information by clicking around the client.