What is API-First? — UK Software Development Guide
Direct Answer
API-First is a software design approach where the API is designed and specified before the implementation. The API contract (typically OpenAPI 3.0) is the primary design artefact — frontend, backend, and third-party consumers all develop against the API specification simultaneously. This contrasts with "API-last" where the API is added after the system is built.
Api-first in the UK
API-First is aligned with UK government digital standards. The GDS API design guide recommends designing APIs before implementation. HMRC Making Tax Digital, NHS APIs, and GOV.UK services all use API-First approaches — their OpenAPI specifications are published before implementations are complete. For ClickMasters projects: API-First means frontend and backend can be developed in parallel (frontend mocks the API using the specification), reducing total project timeline by 20–30% for full-stack builds.
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