sa-api-design

Use this skill whenever work involves designing or reviewing APIs, for example: designing REST API endpoints, defining request/response schemas, choosing HTTP methods and status codes, designing error formats, establishing a versioning strategy, writing API specs or an OpenAPI/Swagger skeleton, reviewing APIs before handoff to developers, designing pagination/filtering/sorting, defining an auth strategy for the API, or analyzing problems in an existing API. Use this skill even if the user does not explicitly say "API Design" — if the intent is to define the contract between client and server, always trigger this skill.