My recent experience with NSwag was really bad... It could only handle the simplest of jsonschema. We were trying to connect with a typescript API that had heavy use of union and product types. Maybe the problem was just that C# doesn't support algebraic typings?

That would track, one of the few things I miss when writing c#. Instead you break out into interfaces as much as you can.

Yeah, the C++/Java/C# family of type systems have obvious holes in them. There are various hacks/implementations for them but since they're not in the core they're not really expected to be supported by random tools either.

Like mentioned, our regular pipe is C# producer (server) and TS consumer (client). Consuming services authored in Java,etc is usually not a problem either but the TS system definetly has a bunch of more cases that aren't easily mapped.

This is what we do. We use kiota to generate clients within other C# services, and orval to generate a client in the frontend. We also run some basic checks against the openapi definition in branch, to detect breaking changes and whatnot.