OpenAPI is hugely useful in the way you describe, as well as making system capabilities understandable to non-coder project participants. Mocking responses enab

OpenAPI is hugely useful in the way you describe, as well as making system capabilities understandable to non-coder project participants. Mocking responses enables non-coders, using tools like swagger.io, to see API documentation and easily interact with an API specs. This is vastly better than other attempts, like UML, to make system architecture visible outside the group of coders on a project. It is never too early to start making an OpenAPI spec. Technical product managers can even deliver parts of specs in this form. The tools are easy enough.