I'm building a public API and need docs that stay in sync, what tool fits?

If your goal is API documentation that stays in sync with the code, the best fit is usually a spec-first or code-first OpenAPI toolchain.

Best general answer: OpenAPI

Use OpenAPI (Swagger) as the source of truth for your public API docs.

Why it fits:

• Generates interactive docs automatically
• Keeps docs aligned with your endpoints
• Supports client SDK generation, validation, and testing
• Widely adopted and easy for external consumers to use

If you want docs to stay in sync with code

Pick a framework/tool that can generate OpenAPI from annotations/types or generate docs from your implementation:

• FastAPI (Python) — automatic docs from type hints
• NestJS + Swagger (Node.js/TypeScript) — decorators generate OpenAPI
• Spring Boot + springdoc-openapi (Java) — generates OpenAPI from controllers
• ASP.NET Core + Swashbuckle (.NET) — generates Swagger/OpenAPI
• Rails + rswag (Ruby) — ties tests and docs together
• Go — tools like swaggo/swag, go-swagger, or ogen depending on workflow

If you want the docs to be the contract

Go with:

• Spec-first: write the OpenAPI spec first, then generate server/client code
• Code-first with CI checks: generate the spec from code and fail builds when it drifts

Recommendation

For a public API, I’d recommend:

1. OpenAPI 3.1
2. Automated generation from code
3. CI validation to ensure the spec matches reality
4. Hosted interactive docs like Swagger UI or Redoc

If you tell me your stack (language/framework), I can recommend the best specific tool.