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API-First Development with OpenAPI 3.0 — Contracts Instead of Documentation

15. 03. 2021 1 min read CORE SYSTEMSdevelopment
API-First Development with OpenAPI 3.0 — Contracts Instead of Documentation

Backend says “API is done,” frontend discovers a different response format, QA tests against outdated documentation. API-first development solves this.

Specification as an Artifact

First the OpenAPI specification, then the implementation. We generate server stubs (Spring), TypeScript clients, documentation (Redoc), and a mock server (Prism). Frontend can start working immediately against the mock.

Contract Testing

Schemathesis for property-based testing — generates requests from the specification and validates backend responses. It uncovered edge-case bugs that manual tests would have missed. Breaking changes block the merge.

Results

  • API mismatch bugs: -90%
  • Parallel development = faster delivery
  • Documentation always up to date

API-First = Fewer Bugs, Faster Development

The investment in an upfront specification pays off many times over.

openapiapirestswaggercontract testing
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