Flask is simple and flexible, FastAPI is modern and fast. It depends on the project.
Comparison¶
- Flask: Minimalist, huge ecosystem, synchronous by default
- FastAPI: Automatic validation, async native, OpenAPI docs
- Performance: FastAPI 2-5x faster thanks to Starlette + async
- Ecosystem: Flask more mature, more extensions
- Learning curve: Flask simpler for beginners
When to Use Flask¶
- Server-side rendered apps (Jinja2 templates)
- Legacy projects and migrations
- Simple prototypes
- Team already knows Flask
When to Use FastAPI¶
- REST/GraphQL API
- Microservices
- High performance / async I/O
- New projects (2024+)
- Type-safe development
Key Takeaway¶
FastAPI for new APIs, Flask for SSR and legacy. Both are great — it depends on the use case.
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