# run_evaluator

> **Function** in `langsmith`

📖 [View in docs](https://reference.langchain.com/python/langsmith/evaluation/evaluator/run_evaluator)

Create a run evaluator from a function.

Decorator that transforms a function into a `RunEvaluator`.

## Signature

```python
run_evaluator(
    func: Callable[[Run, Optional[Example]], Union[_RUNNABLE_OUTPUT, Awaitable[_RUNNABLE_OUTPUT]]],
)
```

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[View source on GitHub](https://github.com/langchain-ai/langsmith-sdk/blob/19be2e470924dde3ca8ac91cc46931d7f899d221/python/langsmith/evaluation/evaluator.py#L432)