api-contract

An API contract is a single source of truth document that defines endpoints, request/response schemas, authentication, and error handling. Create a markdown file in .claude/sprint/[N]/api-contract.md with sections for Base URL, Authentication, Endpoints, TypeScript Interfaces, and Validation Rules to align both teams on the API shape.

API contract validation rules define how requests are validated, what error codes are returned, and how errors are formatted. Include explicit validation rules, error codes, error response schemas, and handling guidelines so frontend and backend teams reference identical requirements.

TypeScript interfaces in an API contract ensure type safety across backend and frontend by defining request/response shapes. Define interfaces for each endpoint's input and output, making them accessible to both teams so types stay synchronized during implementation.

Yes. An API contract serves as documentation for all endpoints, request/response schemas, and error codes, making it the reference for QA testing, feature development, migrations, and validation across the entire API lifecycle.

An API contract specifies Base URL, API versioning strategy, authentication method, required headers, pagination approach, and rate-limiting rules. These core requirements ensure both teams implement consistent endpoints and handle requests identically.

Use an API contract when backend and frontend teams need a single validated reference that prevents misalignment on endpoints, data types, error codes, and validation logic. It replaces scattered documentation with a structured source of truth updated alongside feature changes.