FastAPI vs Flask: Complete Comparison Guide
Compare FastAPI and Flask on performance, type validation, documentation, and async support. Discover which Python framework is the best fit for your API project.
FastAPI
A modern Python framework for building fast APIs with automatic documentation and type validation. FastAPI leverages Python type hints and Pydantic to automatically validate requests and generates interactive API documentation via Swagger UI and ReDoc. It is async-native and one of the fastest Python frameworks.
Flask
A lightweight Python micro-framework offering maximum flexibility with a minimal core. Flask imposes no choices for databases, validation, or templating and lets developers pick their own tools. It has been widely deployed for web applications and APIs for over fifteen years thanks to its simple, familiar API.
Comparison table
| Feature | FastAPI | Flask |
|---|---|---|
| Performance | Async-native — up to 2-3x faster than Flask for I/O tasks | Synchronous — suitable for standard web applications |
| Type validation | Automatic via Pydantic — errors caught before processing | Manual via Marshmallow, WTForms, or custom validation |
| API documentation | Auto-generated — Swagger UI and ReDoc out of the box | Manual via Flask-RESTx, Flasgger, or other extensions |
| Async support | Native async/await — designed for concurrency | Limited — async possible since Flask 2.0 but not native |
| Learning curve | Low — minimal API, type hints make code self-documenting | Very low — one of the simplest Python frameworks |
| Ecosystem | Growing — increasingly more extensions and community packages | Mature — hundreds of extensions for every need |
Verdict
FastAPI is the clear choice for new API projects in Python. Its automatic documentation, type validation via Pydantic, and async support make it superior to Flask for API development. Flask remains relevant for simple web applications with server-side rendering and for projects where the extensive extension library is indispensable. For teams building an API in 2026, FastAPI has become the standard. Flask is the right tool when simplicity and a proven ecosystem take priority over performance.
Our recommendation
At MG Software, we advise Python teams to choose FastAPI for new API projects. The automatic OpenAPI documentation and Pydantic validation significantly reduce development time and errors. We recommend Flask for simple web applications or when a team already has extensive Flask experience. In our own stack, we fulfill the same need with Fastify and TypeScript, which provides similar benefits to FastAPI — type safety, high performance, and automatic schema generation.
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