# VertexStringEvaluator

> **Class** in `langchain_google_vertexai`

📖 [View in docs](https://reference.langchain.com/python/langchain-google-vertexai/evaluators/evaluation/VertexStringEvaluator)

Evaluate the perplexity of a predicted string.

## Signature

```python
VertexStringEvaluator(
    self,
    metric: str,
    **kwargs = {},
)
```

## Extends

- `_EvaluatorBase`
- `StringEvaluator`

## Constructors

```python
__init__(
    self,
    metric: str,
    **kwargs = {},
) -> None
```

| Name | Type |
|------|------|
| `metric` | `str` |


## Methods

- [`evaluate()`](https://reference.langchain.com/python/langchain-google-vertexai/evaluators/evaluation/VertexStringEvaluator/evaluate)

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[View source on GitHub](https://github.com/langchain-ai/langchain-google/blob/a3f016b2a6c4af535df275545f76fa7424aa39e5/libs/vertexai/langchain_google_vertexai/evaluators/evaluation.py#L180)