FastAPI Backend Skill

Use when adding endpoints, schemas, dependencies, or middleware.

Conventions

• •Pydantic v2 for request/response models
• •APIRouter per domain
• •Validate input at the boundary
• •Return JSON with a consistent envelope when useful

Example response model:

from pydantic import BaseModel
from typing import Generic, Optional, TypeVar

T = TypeVar("T")

class ApiResponse(BaseModel, Generic[T]):
    success: bool
    data: Optional[T] = None
    error: Optional[str] = None

Preferred structure (when ready)

• •app/main.py
• •app/api/routes/
• •app/schemas/
• •app/services/
• •app/db/
• •tests/

Error handling

• •Use HTTPException for expected errors
• •Add a global exception handler for unexpected errors

Testing

• •Use pytest + httpx.AsyncClient for route tests
• •Keep tests close to domain modules