[danappelxx]

I suspect OpenAPI advocates would argue you should start with the spec and use it to generate both the client and server. This is already a common pattern in other RPC definition languages such as gRPC. You _could_ write a server to match the gRPC spec, but why would you?

[lolinder]

That works great if you're starting from scratch, but not so much if you're on a brownfield project. The way the generators are written, even generating a new endpoint can't be done after code has been written because it generates a whole file with route stubs.

[danappelxx]

Agreed, but if you’re asking for a solution that will generate a spec from your code, the more proven path is to generate code from a spec. Gives you more and costs less.

In my opinion the problem is that there’s some APIs that are impossible to represent with OpenAPI — that’s the real challenge they should be solving with this version, not reducing spec line count.

[clintonb]

Not sure if I’m an advocate, but definitely a fan. I use frameworks (e.g., Django REST Framework, Nest.js) to build the server and generate my OpenAPI spec. I find it faster than writing YAML/JSON manually, and I end up with a half-working server at the end of it all.

[bcoughlan]

It depends on your use case. Starting with the spec can unblock other implementers, so that they can work with mocks while you build the implementation. And it can help prevent re-work by describing the API first and getting feedback.

Bigger orgs also have style guides for public APIs and you can use various linters/standardization tools to enforce this. Tech writers can work on the API documentation without making changes in your code. There are tools that can tell you if your spec changes would cause breaking changes to API clients, such as adding a required query parameter.

You might not need these things on your project, but for some users it makes sense to write the spec first.

[clintonb]

I’m familiar with all that. I worked at Stripe, where I started with a skeleton server first.

My point is, when I work with a framework that generates an OpenAPI spec, I find it faster to generate the spec from a prototype server than to write the spec by hand.