fastapi

FastAPI has been solid for production APIs from a security perspective. The tight integration with Pydantic means input validation is automatic and type-safe—you define request models and FastAPI validates everything before your code runs. This prevents entire classes of injection attacks by default. The automatic OpenAPI schema generation is helpful for security reviews since you can see exactly what inputs are expected.

Authentication is well-designed with the OAuth2 flows built-in and dependency injection pattern for auth checks. The security utilities for password hashing (passlib integration) and JWT handling work well, though you need to configure them carefully. Error handling is generally good—validation errors don't leak internal details, though you'll want to customize exception handlers for production to avoid exposing stack traces in debug mode.

The main security concern is the dependency tree—Starlette, Pydantic, plus optional dependencies for features like jinja2 or python-multipart. You need active CVE monitoring. TLS is handled at the ASGI server level (uvicorn/hypercorn), which is appropriate but means security configuration lives elsewhere.

FastAPI feels like magic when you first use it. You define a function with type hints, add a decorator, and suddenly you have automatic request validation, serialization, and interactive API docs at /docs. The learning curve is incredibly gentle - if you know Python type hints and basic function decorators, you're 80% there. I've onboarded junior developers who had working endpoints within an hour.

The error messages are outstanding. When Pydantic validation fails, you get detailed JSON responses showing exactly which fields failed and why. During development, stack traces clearly point to your code, not framework internals. The dependency injection system initially seems like 'yet another concept to learn' but it's actually intuitive once you realize dependencies are just functions that return values.

Documentation is stellar with a tutorial that builds progressively and a comprehensive user guide covering authentication, database integration, background tasks, and testing. Common tasks like file uploads, form data, and headers are straightforward. The community is responsive - most StackOverflow questions have quality answers, and GitHub issues get attention quickly. Debugging is painless because the framework stays out of your way.

FastAPI delivers on its performance promises in production. The ASGI foundation handles high concurrency well, and async/await support integrates cleanly with existing async libraries. Dependency injection system is genuinely useful for managing database connections, Redis pools, and other resources. The automatic OpenAPI schema generation isn't just a nice-to-have - it's saved countless hours of API documentation drift.

Operationally, it's solid but requires understanding. Response timeouts need explicit configuration via Uvicorn/Hypercorn settings, not FastAPI itself. Background tasks work well for fire-and-forget operations but you'll need Celery/RQ for anything more robust. Exception handlers are straightforward to customize, and middleware hooks provide good observability points for metrics and tracing. Memory footprint stays reasonable under load.

The ecosystem maturity shows. Starlette foundation is stable, but watch for breaking changes in minor versions (validation behavior shifted between 0.95-0.100). Testing with TestClient works well though async test clients require extra setup. Overall, it's my go-to for async Python APIs but demands attention to resource lifecycle management.