Start with a clear contract
Define the endpoint purpose, request structure, parameters, validation rules, lookup dependencies and response behavior before implementation.
Keep validation explicit
Validation should cover invalid values, incompatible combinations and lookup dependencies. Clear error responses make APIs easier to consume and troubleshoot.
Document lookup dependencies
If a parameter such as an ID must be obtained from another endpoint, document that relationship so consumers know where the value comes from.
Design for consistency
Consistent naming, status handling, authorization, error structures and documentation reduce integration effort across a large API surface.