fastapi

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FastAPI Python async framework with Pydantic and automatic OpenAPI. Use for Python APIs.

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Sourceg1joshi/agent-skills

Added on2026-02-11

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npx skill4agent add g1joshi/agent-skills fastapi

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FastAPI

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints. It is one of the fastest Python frameworks available.

When to Use

APIs: The default choice for modern Python APIs.
Machine Learning: Native integration with Pydantic makes JSON <-> Model interaction seamless.
Performance: Built on Starlette and Pydantic v2, it rivals Node.js and Go in benchmarks.

Quick Start

python

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

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

Core Concepts

Pydantic Models

Define data shape using Python classes. Validation and JSON serialization happen automatically.

Dependency Injection

FastAPI has a powerful DI system.

async def read_users(db: Session = Depends(get_db)):

.

OpenAPI (Swagger)

Automatically generates interactive API documentation at

/docs

.

Best Practices (2025)

Do:

Use Pydantic v2: Ensure you are on v2 for the massive Rust-based performance boost.
Use
lifespan
: Use the new
```
lifespan
```
context manager for startup/shutdown events instead of deprecated
```
on_event
```
.
Type Everything: The more you type, the better the auto-generated docs and validation.

Don't:

Don't block the loop: Run CPU bound code (image processing, heavy math) in
```
def
```
endpoints (threadpool), not
```
async def
```
(event loop), or use background tasks.

References

FastAPI Documentation