# PairwiseStringEvaluator

> **Class** in `langchain_classic`

📖 [View in docs](https://reference.langchain.com/python/langchain-classic/evaluation/schema/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-classic/evaluation/schema/PairwiseStringEvaluator/evaluate_string_pairs)
- [`aevaluate_string_pairs()`](https://reference.langchain.com/python/langchain-classic/evaluation/schema/PairwiseStringEvaluator/aevaluate_string_pairs)

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[View source on GitHub](https://github.com/langchain-ai/langchain/blob/02991cb4cf2063d51a07268edafb05fe53de1826/libs/langchain/langchain_classic/evaluation/schema.py#L265)