What is API Contract? — UK Software Development Guide
Direct Answer
An API contract is a formal specification of how an API behaves — defining: available endpoints, request formats, response formats, error codes, and authentication requirements. An API contract serves as a binding agreement between API producer (the service exposing the API) and API consumers (clients that call the API). OpenAPI 3.0 is the standard format for documenting REST API contracts.
Api-contract in the UK
API contracts have commercial and compliance significance for UK software. Commercially: a published API contract is a commitment to backward compatibility — breaking changes to the contract without adequate deprecation notice can breach service agreements and create FCA or NHS compliance incidents. UK GDPR: the API contract should define which endpoints return personal data — enabling data flow documentation for Article 30 Records of Processing Activities. ClickMasters delivers OpenAPI 3.0 contracts for all REST APIs as a standard deliverable, with semantic versioning to communicate breaking changes.
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