Quick Comparison
| Flask | FastAPI | |
|---|---|---|
| Async | No (WSGI) | Yes (ASGI) |
| Type hints | Optional | Required (used for validation) |
| API docs | Manual | Auto-generated |
| Performance | Good | Better (async) |
| Ecosystem | Massive | Growing fast |
When to Use Flask
- Simple web apps and APIs
- You want maximum flexibility
- Your team knows Flask
- You need Flask-specific extensions
When to Use FastAPI
- New API projects
- You want automatic validation from type hints
- You need async support
- You want auto-generated Swagger docs
Verdict
FastAPI for new API projects — it’s faster, has better DX, and auto-generates docs. Flask if you’re maintaining existing code or need its specific extensions.