# pydantic.errors.ConfigError: Invalid validator signature

- **ID:** `python/pydantic-validator-wrong-signature`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A @field_validator or @model_validator function has an incorrect number or names of arguments (e.g., missing cls or value).

## Version Compatibility

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

## Workarounds

1. **** (95% success)
   ```
   Define correctly: @field_validator('field') def validate(cls, v): return v
   ```
2. **** (90% success)
   ```
   For model validator: @model_validator(mode='after') def validate(self): return self
   ```

## Dead Ends

- **** — Pydantic expects at least two arguments: cls and value. (90% fail)
- **** — Validators are class methods, not instance methods. (80% fail)