openapi-spec-generation

FastAPI generates OpenAPI automatically from Pydantic models and route decorators. Define models with Field validation, set response_model and status_code on endpoints, then export the spec as JSON via app.openapi().

tsoa generates OpenAPI specs from TypeScript decorators like @Route, @Get, @Security, and @Response on controller classes. Interfaces and enums in your code become component schemas in the generated specification.

Design-first writes the OpenAPI spec before any code, suiting new APIs and contract-driven teams. Code-first generates the spec from annotated code, fitting existing APIs, while hybrid approaches annotate code to keep both in sync.

Run spectral lint with a .spectral.yaml ruleset extending spectral:oas to enforce operationIds, descriptions, and naming conventions. Redocly offers redocly lint with rules like no-invalid-media-type-examples and MIME type enforcement.

Yes, openapi-generator-cli generates clients from a spec for TypeScript (typescript-fetch), Python, and Go. Pass the spec file with -i, choose a generator with -g, and set output options via additional-properties.

Avoid code-first when multiple teams must agree on a contract before implementation, since the spec becomes an artifact of code rather than an agreed design. Design-first is better for new APIs requiring upfront consumer alignment.