Agent skill

fastapi-helper

FastAPI development assistant for building modern Python web APIs. Provides guidance on routing, request/response handling, dependency injection, authentication, middleware, WebSockets, testing, and Pydantic models. Use when: (1) Creating FastAPI applications or endpoints, (2) Implementing CRUD operations, (3) Setting up authentication/authorization, (4) Working with request parameters (path, query, body, headers, cookies, forms, files), (5) Configuring middleware or CORS, (6) Implementing WebSocket connections, (7) Writing tests for FastAPI apps, (8) Defining Pydantic models for validation.

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npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/fastapi-helper

SKILL.md

FastAPI Helper

Build modern, high-performance Python APIs with FastAPI.

Quick Start

python
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def root():
    return {"message": "Hello World"}

Run: uvicorn main:app --reload

Core Concepts

Route Decorators

Decorator HTTP Method
@app.get() GET
@app.post() POST
@app.put() PUT
@app.delete() DELETE
@app.patch() PATCH

Parameter Functions

Function Source
Path() URL path /items/{id}
Query() Query string ?q=foo
Body() JSON body
Header() HTTP headers
Cookie() Cookies
Form() Form data
File() / UploadFile File uploads

Dependency Injection

python
from fastapi import Depends

async def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

@app.get("/items/")
async def read_items(db: Session = Depends(get_db)):
    return db.query(Item).all()

Common Imports

python
from fastapi import (
    FastAPI, APIRouter, Depends, HTTPException, status,
    Request, Response, BackgroundTasks, WebSocket,
    Path, Query, Body, Header, Cookie, Form, File, UploadFile
)
from fastapi.responses import JSONResponse, HTMLResponse, FileResponse, RedirectResponse
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel, Field, EmailStr

Reference Documentation

Load these based on task:

Task Reference File
Routes, APIRouter, decorators references/routing.md
Path, Query, Body, Form, File params references/parameters.md
Response types, status codes, headers references/responses.md
Depends, Security, OAuth2 references/dependencies.md
Middleware, CORS, lifespan, BackgroundTasks references/middleware-events.md
WebSocket connections references/websockets.md
HTTPException, error handlers references/exceptions.md
Pydantic models, validation references/pydantic-models.md
TestClient, pytest fixtures references/testing.md

Common Patterns

CRUD Endpoint Structure

python
from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.orm import Session

router = APIRouter(prefix="/items", tags=["items"])

@router.get("/", response_model=list[ItemOut])
async def list_items(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
    return db.query(Item).offset(skip).limit(limit).all()

@router.get("/{item_id}", response_model=ItemOut)
async def get_item(item_id: int, db: Session = Depends(get_db)):
    item = db.query(Item).filter(Item.id == item_id).first()
    if not item:
        raise HTTPException(status_code=404, detail="Item not found")
    return item

@router.post("/", response_model=ItemOut, status_code=status.HTTP_201_CREATED)
async def create_item(item: ItemCreate, db: Session = Depends(get_db)):
    db_item = Item(**item.model_dump())
    db.add(db_item)
    db.commit()
    db.refresh(db_item)
    return db_item

@router.put("/{item_id}", response_model=ItemOut)
async def update_item(item_id: int, item: ItemUpdate, db: Session = Depends(get_db)):
    db_item = db.query(Item).filter(Item.id == item_id).first()
    if not db_item:
        raise HTTPException(status_code=404, detail="Item not found")
    for key, value in item.model_dump(exclude_unset=True).items():
        setattr(db_item, key, value)
    db.commit()
    return db_item

@router.delete("/{item_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_item(item_id: int, db: Session = Depends(get_db)):
    db_item = db.query(Item).filter(Item.id == item_id).first()
    if not db_item:
        raise HTTPException(status_code=404, detail="Item not found")
    db.delete(db_item)
    db.commit()

CORS Setup

python
from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["http://localhost:3000"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

JWT Authentication Pattern

python
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

async def get_current_user(token: str = Depends(oauth2_scheme)):
    user = decode_token(token)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid credentials",
            headers={"WWW-Authenticate": "Bearer"},
        )
    return user

@app.get("/users/me")
async def read_users_me(current_user: User = Depends(get_current_user)):
    return current_user

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