It would be helpful if OpenAPI specification allowed me to specify certain responses that will be returned for every endpoint in the specification, rather than having to document every response on every endpoint. (Although I would imagine people might want to apply those default responses to some sort of pattern matching, either by path or tag or other...)

For instance, if my API requires authentication on every endpoint, applies rate limiting to every endpoint, and can return a 500 Internal Server Error for every endpoint, then it would be nice to define a default set of responses for 401, 403, 429 and 500. Those responses would also include e.g. rate limit headers.

When following a design-first approach, this would significantly reduce the amount of copy-pasting of response references, reduce the chance of making errors, and reduce size of a fully-documented OpenAPI specification, which then decreases the resources required to process one when generating client-side docs.