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FastAPI: Modern Python APIs at lightning speed

FastAPI is a Python web framework for building APIs that is blazingly fast, automatically generates documentation, and catches errors before your code runs…

Overview

FastAPI is one of the fastest Python web frameworks available (on par with Node.js and Go in benchmarks). It uses Python's type hint system to automatically validate incoming data, generate OpenAPI documentation, and provide editor autocomplete. Built for the modern AI era, FastAPI is used at major companies like Microsoft, Uber, and Netflix for serving ML models and backend APIs.

Core concepts

Path operations: Decorate functions with @app.get(), @app.post() etc. to define your API endpoints. Pydantic models: Define your data shapes as Python classes. FastAPI auto-validates and auto-documents them. Automatic docs: Visit /docs for Swagger UI and /redoc for ReDoc — both generated automatically from your code. Async support: Use async def for non-blocking endpoints that can handle thousands of concurrent requests.

When to use FastAPI

Building a Python API that needs to be fast Serving machine learning or AI models Any API where automatic documentation saves time Teams already using Python and Pydantic

Quick-start tip

After running your FastAPI app, navigate to `/docs` in the Preview to see an interactive Swagger UI — you can test every endpoint right from the browser, no extra tools needed.