12. Interactive API Documentation with /docs

Automatic OpenAPI Specification Generation

FastAPI generates OpenAPI specifications directly from executable code using type hints, request models, and response schemas. Because the same definitions drive both runtime behavior and documentation, the specification remains accurate by design. This eliminates the common problem of outdated or misleading API docs.

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Swagger UI vs ReDoc

Swagger UI provides an interactive interface for exploring and executing API endpoints directly from the browser. ReDoc focuses on structured, readable documentation optimized for long-form reference. FastAPI supports both, allowing teams to choose based on whether interactivity or documentation clarity is the priority.

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Using /docs for Development and Debugging

The /docs endpoint functions as a live development and testing environment. Developers can validate request schemas, inspect responses, and observe validation errors without external tools. This tight feedback loop accelerates debugging and encourages correct API usage early in the development cycle.