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Getting Started

FastAPI is a modern, high-performance web framework for building APIs with Python, based on standard Python type hints. It is designed to be easy to use, fast to code, and ready for production.

Prerequisites​

  • Python: Version 3.10 or higher is required.
  • Virtual Environment: It is highly recommended to use a virtual environment (e.g., venv, uv, or pdm) to manage your dependencies.

Installation​

The recommended way to install FastAPI is with the standard group of optional dependencies, which includes a high-performance ASGI server (uvicorn) and the FastAPI CLI.

pip install "fastapi[standard]"

If you prefer a minimal installation without the CLI and extra dependencies, you can use:

pip install fastapi

Quick Start​

1. Create your application​

Create a file named main.py and add the following code:

from fastapi import FastAPI

# Initialize the FastAPI application
app = FastAPI()

@app.get("/")
async def read_root():
    """
    A simple GET endpoint that returns a JSON response.
    """
    return {"Hello": "World"}

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: str | None = None):
    """
    An endpoint with path and query parameters.
    FastAPI automatically validates that item_id is an integer.
    """
    return {"item_id": item_id, "q": q}

2. Run the development server​

Use the fastapi dev command to start the server with auto-reload enabled:

fastapi dev main.py

The server will start at http://127.0.0.1:8000.

3. Interactive API Documentation​

FastAPI automatically generates interactive documentation for your API. Once the server is running, you can access:

Usage with Pydantic​

FastAPI uses Data Schemas and Validation for data validation and serialization. You can define complex request bodies using Python classes:

from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None

app = FastAPI()

@app.post("/items/")
async def create_item(item: Item):
    return {"item_name": item.name, "item_price": item.price}

Verify Installation​

To confirm that FastAPI and its CLI are correctly installed, run:

fastapi --version

Other Install Options​

If you use the uv package manager, you can install FastAPI and run it immediately:

uv add "fastapi[standard]"
uv run fastapi dev main.py

Production Deployment​

For production, use the fastapi run command, which optimizes the server configuration:

fastapi run main.py

Next Steps​

  • Explore the tutorial to learn about dependency injection, security, and more.
  • Learn how to structure Bigger Applications using APIRouter.
  • Check out the deployment guide for hosting your API on various platforms.