fastapi-expert

name fastapi-expert description Use when building high-performance async Python APIs with FastAPI and Pydantic V2. Invoke to create REST endpoints, define Pydantic models, implement authentication flows, set up async SQLAlchemy database operations, add JWT authentication, build WebSocket endpoints, or generate OpenAPI documentation. Trigger terms: FastAPI, Pydantic, async Python, Python API, REST API Python, SQLAlchemy async, JWT authentication, OpenAPI, Swagger Python. license MIT metadata {"author":"https://github.com/Jeffallan","version":"1.1.0","domain":"backend","triggers":"FastAPI, Pydantic, async Python, Python API, REST API Python, SQLAlchemy async, JWT authentication, OpenAPI, Swagger Python","role":"specialist","scope":"implementation","output-format":"code","related-skills":"fullstack-guardian, django-expert, test-master"} FastAPI Expert Deep expertise in async Python, Pydantic V2, and production-grade API development with FastAPI. When to Use This Skill Building REST APIs with FastAPI Implementing Pydantic V2 validation schemas Setting up async database operations Implementing JWT authentication/authorization Creating WebSocket endpoints Optimizing API performance Core Workflow Analyze requirements — Identify endpoints, data models, auth needs Design schemas — Create Pydantic V2 models for validation Implement — Write async endpoints with proper dependency injection Secure — Add authentication, authorization, rate limiting Test — Write async tests with pytest and httpx; run pytest after each endpoint group and verify OpenAPI docs at /docs Checkpoint after each step: confirm schemas validate correctly, endpoints return expected HTTP status codes, and /docs reflects the intended API surface before proceeding. Minimal Complete Example Schema + endpoint + dependency injection in one cohesive unit: # schemas.py from pydantic import BaseModel, EmailStr, field_validator, model_config class UserCreate ( BaseModel ): model_config = model_config(str_strip_whitespace= True ) email: EmailStr password: str name: str | None = None @field_validator( "password" ) @classmethod def password_strength ( cls, v: str ) -> str : if len (v) < 8 : raise ValueError( "Password must be at least 8 characters" ) return v class UserResponse ( BaseModel ): model_config = model_config(from_attributes= True ) id : int email: EmailStr name: str | None = None # routers/users.py from fastapi import APIRouter, Depends, HTTPException, status from sqlalchemy.ext.asyncio import AsyncSession from typing import Annotated from app.database import get_db from app.schemas import UserCreate, UserResponse from app import crud router = APIRouter(prefix= "/users" , tags=[ "users" ]) DbDep = Annotated[AsyncSession, Depends(get_db)] @router.post( "/" , response_model=UserResponse, status_code=status.HTTP_201_CREATED ) async def create_user ( payload: UserCreate, db: DbDep ) -> UserResponse: existing = await crud.get_user_by_email(db, payload.email) if existing: raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail= "Email already registered" ) return await crud.create_user(db, payload) # crud.py from sqlalchemy import select from sqlalchemy.ext.asyncio import AsyncSession from app.models import User from app.schemas import UserCreate from app.security import hash_password async def get_user_by_email ( db: AsyncSession, email: str ) -> User | None : result = await db.execute(select(User).where(User.email == email)) return result.scalar_one_or_none() async def create_user ( db: AsyncSession, payload: UserCreate ) -> User: user = User(email=payload.email, hashed_password=hash_password(payload.password), name=payload.name) db.add(user) await db.commit() await db.refresh(user) return user JWT Authentication Snippet # security.py from datetime import datetime, timedelta, timezone from jose import JWTError, jwt from fastapi import Depends, HTTPException, status from fastapi.security import OAuth2PasswordBearer from typing import Annotated SECRET_KEY = "read-from-env" # use os.environ / settings ALGORITHM = "HS256" oauth2_scheme = OAuth2PasswordBearer(tokenUrl= "/auth/token" ) def create_access_token ( subject: str , expires_delta: timedelta = timedelta( minutes= 30 ) ) -> str : payload = { "sub" : subject, "exp" : datetime.now(timezone.utc) + expires_delta} return jwt.encode(payload, SECRET_KEY, algorithm=ALGORITHM) async def get_current_user ( token: Annotated[ str , Depends( oauth2_scheme )] ) -> str : try : data = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM]) subject: str | None = data.get( "sub" ) if subject is None : raise ValueError return subject except (JWTError, ValueError): raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail= "Invalid credentials" ) CurrentUser = Annotated[ str , Depends(get_current_user)] Reference Guide Load detailed guidance based on context: Topic Reference Load When Pydantic V2 references/pydantic-v2.md Creating schemas, validation, model_config SQLAlchemy references/async-sqlalchemy.md Async database, models, CRUD operations Endpoints references/endpoints-routing.md APIRouter, dependencies, routing Authentication references/authentication.md JWT, OAuth2, get_current_user Testing references/testing-async.md pytest-asyncio, httpx, fixtures Django Migration references/migration-from-django.md Migrating from Django/DRF to FastAPI Constraints MUST DO Use type hints everywhere (FastAPI requires them) Use Pydantic V2 syntax ( field_validator , model_validator , model_config ) Use Annotated pattern for dependency injection Use async/await for all I/O operations Use X | None instead of Optional[X] Return proper HTTP status codes Document endpoints (auto-generated OpenAPI) MUST NOT DO Use synchronous database operations Skip Pydantic validation Store passwords in plain text Expose sensitive data in responses Use Pydantic V1 syntax ( @validator , class Config ) Mix sync and async code improperly Hardcode configuration values Output Templates When implementing FastAPI features, provide: Schema file (Pydantic models) Endpoint file (router with endpoints) CRUD operations if database involved Brief explanation of key decisions Knowledge Reference FastAPI, Pydantic V2, async SQLAlchemy, Alembic migrations, JWT/OAuth2, pytest-asyncio, httpx, BackgroundTasks, WebSockets, dependency injection, OpenAPI/Swagger Documentation