FastAPI Cursor Rules Template

---
description: "Routes & Endpoints"
alwaysApply: false
---
- Use path operation decorators (@app.get, @app.post, etc.).
- Use      spaces for indentation.
- Use snake_case for route handler functions.
- Use Pydantic models for request bodies and query parameters.
- Use path parameters with type hints for automatic validation.
- Use APIRouter for modular route organization with prefix and tags.

---
description: "Validation & Schemas"
alwaysApply: false
---
- Use Pydantic v2 models for all request/response schemas.
- Use Field() with validation constraints (min_length, gt, pattern, etc.).
- Define separate schemas for input (BaseModel) and output (Response model).
- Use response_model parameter for automatic response serialization.
- Use Annotated types with Query(), Path(), Body(), Header().
- Use model_validator for cross-field validation logic.

---
description: "Dependency Injection"
alwaysApply: false
---
- Use Depends() for reusable dependencies (DB sessions, auth, config).
- Use generator-based dependencies with yield for resource cleanup.
- Use dependency overrides for testing.
- Use sub-dependencies — dependencies that depend on other dependencies.
- Keep dependencies focused on a single concern.
- Use class-based dependencies via __call__ for stateful dependencies.

---
description: "Error Handling"
alwaysApply: false
---
- Use HTTPException for standard HTTP error responses.
- Define custom exception handlers with @app.exception_handler().
- Use status_code constants from fastapi.status.
- Return structured error responses with detail and optional headers.
- Use background tasks (BackgroundTasks) for non-critical side effects.
- Log exceptions with traceback in exception handlers.