> ## Documentation Index
> Fetch the complete documentation index at: https://arizeai-433a7140.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Regex Match

> Check whether a text matches a regular expression pattern.

Checks whether a text matches a regular expression pattern. By default, the pattern is searched anywhere in the text (partial match). Returns `true` if the pattern matches, `false` otherwise.

## Parameters

| Parameter    | Type    | Required | Default | Description                                                                                                 |
| ------------ | ------- | -------- | ------- | ----------------------------------------------------------------------------------------------------------- |
| `pattern`    | string  | Yes      | —       | The regular expression pattern to match                                                                     |
| `text`       | string  | Yes      | —       | The text to search                                                                                          |
| `full_match` | boolean | No       | `false` | If `true`, the pattern must match the entire string; if `false`, a match anywhere in the text is sufficient |

## Output

| Property     | Value             | Description                                     |
| ------------ | ----------------- | ----------------------------------------------- |
| `label`      | `true` or `false` | Whether the pattern matched                     |
| `score`      | `1.0` or `0.0`    | Numeric score (`1.0` = match, `0.0` = no match) |
| Optimization | Maximize          | Higher scores are better                        |

## Configuring Inputs

Each evaluator parameter can be set to either a **path** (a JSONPath expression that extracts a value from the evaluation parameters) or a **literal** (a fixed value typed directly). Use paths to pull from dataset inputs, task outputs, reference data, or metadata. Use literals for static configuration like regex patterns.

See [Input Mapping](/docs/phoenix/evaluation/server-evals/input-mapping) for full details on mapping modes, resolution order, and examples.

## Usage Examples

**Format compliance** — A model that must produce output in a specific structural format (a date, phone number, or identifier). **Pattern** is the regular expression defining the required format, set as a literal value. **Text** is the model's output field — use a direct path for a plain string response, or a nested path like `output.date` if the target value is embedded in a JSON object.

**Citation or reference checking** — A RAG pipeline that must include a URL, citation marker, or other structured element in every response. **Pattern** matches the expected element (e.g., a URL regex or citation format); **Text** is the model's full response. Partial match mode (the default) passes as long as the pattern appears anywhere in the output.

**Output type gating** — A code assistant whose output should contain a function definition rather than prose. **Pattern** is anchored to the expected code structure; **Text** is the response field. If your model returns structured JSON with a `code` key, map **Text** to `output.code` rather than the entire response.

## Notes

<Warning>
  Complex regex patterns can be slow on long inputs. Avoid patterns with nested quantifiers or excessive backtracking (e.g., `(a+)+`, `.*.*`). Prefer anchored patterns and specific character classes over broad wildcards. Test your pattern against representative inputs before deploying to a large dataset.
</Warning>

## See Also

* [Pre-Built Metrics Overview](/docs/phoenix/evaluation/server-evals/pre-built-metrics)
* [Contains](/docs/phoenix/evaluation/server-evals/pre-built-metrics/contains) — check whether a text contains specific words
* [Exact Match](/docs/phoenix/evaluation/server-evals/pre-built-metrics/exact-match) — check whether two strings are identical