---
name: fastapi-pydantic-v2
description: Writes modern FastAPI endpoints using Pydantic v2 syntax and Annotated dependencies. Use whenever generating or refactoring API routes.
---
# FastAPI & Pydantic v2 Standards

## Pydantic v2 Rules
- NEVER use `.dict()` or `.json()`. ALWAYS use `.model_dump()` and `.model_dump_json()`.
- NEVER use `@validator` or `@root_validator`. ALWAYS use `@field_validator` and `@model_validator(mode="before|after")`.
- NEVER use `schema_extra`. Use `json_schema_extra` inside the `model_config` dict.
- Use `pydantic_settings.BaseSettings` for all environment variable configurations.

## FastAPI Rules
- ALWAYS use `typing.Annotated` for dependency injection (e.g., `db: Annotated[AsyncSession, Depends(get_db)]`).
- Do not use `def` for endpoints that perform I/O; always use `async def`.
- Raise `fastapi.HTTPException` for expected client errors instead of returning standard dictionaries.