# PairwiseStringEvaluator

> **Class** in `langchain_google_vertexai`

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

Compare the output of two models (or two outputs of the same model).

## Signature

```python
PairwiseStringEvaluator()
```

## Extends

- `_EvalArgsMixin`
- `ABC`

## Methods

- [`evaluate_string_pairs()`](https://reference.langchain.com/python/langchain-google-vertexai/evaluators/_core/PairwiseStringEvaluator/evaluate_string_pairs)
- [`aevaluate_string_pairs()`](https://reference.langchain.com/python/langchain-google-vertexai/evaluators/_core/PairwiseStringEvaluator/aevaluate_string_pairs)

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[View source on GitHub](https://github.com/langchain-ai/langchain-google/blob/a3f016b2a6c4af535df275545f76fa7424aa39e5/libs/vertexai/langchain_google_vertexai/evaluators/_core.py#L191)