"The generated client keeps calling DELETE /items/{id}." "The server returns 405 Method Not Allowed." An OpenAPI spec is not just documentation. SDKs, frontend types, API docs, mock servers — everything is generated from the spec. When the implementation drifts from it, everything generated starts lying quietly . This is about oas-drift , a CLI I built that detects that drift — with zero dependencies (Python 3.11+ standard library only, no LLM). https://github.com/sunnydachs/o...