# PydanticUserError: @field_validator on 'email' requires a classmethod, but the decorator was applied to a regular method. Add @classmethod below @field_validator.

- **ID:** `python/pydantic-validator-not-classmethod`
- **Domain:** python
- **Category:** runtime_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

In Pydantic v2, field_validator must decorate a classmethod; omitting @classmethod causes a PydanticUserError at class definition time.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 2.x | active | — | — |

## Workarounds

1. **** (99% success)
   ```
   from pydantic import field_validator
class User(BaseModel):
    email: str
    @field_validator('email')
    @classmethod
    def check_email(cls, v):
        return v.lower()
   ```
2. **** (94% success)
   ```
   from typing import Annotated
from pydantic import AfterValidator
Email = Annotated[str, AfterValidator(lambda v: v.lower())]
   ```

## Dead Ends

- **** — field_validator explicitly checks for classmethod; staticmethod is rejected. (95% fail)
- **** — Validators must be defined inside the model class to be registered. (90% fail)