# metric

Learn about the metric extension point.

{% hint style="info" %}
Heads up!

When writing conditions, be sure to use floating-point numbers. For example, use `"== 8.0"` instead of `"== 8"`.
{% endhint %}

| Name        | Type     | Description                                                    |
| ----------- | -------- | -------------------------------------------------------------- |
| `formula`   | `string` | A formula of pre-defined variables to be evaluated.            |
| `condition` | `string` | A binary condition upon which `formula` will trigger an alert. |

`metric` enforces arbitrary formulas based on pre-defined, built-in variables.

```yaml
extends: metric
message: 'Try to keep the Flesch-Kincaid grade level (%s) below 8.'
link: |
  https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests

formula: |
  (0.39 * (words / sentences)) + (11.8 * (syllables / words)) - 15.59

condition: '> 8.0'
```

## [Variables](#variables)

The table below summarizes all available variables:

|       Variable       |                                    Description                                   |
| :------------------: | :------------------------------------------------------------------------------: |
|     `blockquote`     |                         The number of `blockquote` tags.                         |
|     `characters`     |                             The number of characters.                            |
|    `complex_words`   | The number of polysyllabic words without common suffixes (`es`, `ed`, `ing`, …). |
|    `heading.h{n}`    |    The number of headings at the specified level (for example, `heading.h1`).    |
|        `list`        |                         The number of `ol` and `ul` tags.                        |
|     `long_words`     |                 The number of words with more than 6 characters.                 |
|     `paragraphs`     |                             The number of paragraphs.                            |
| `polysyllabic_words` |                  The number of words with more than 2 syllables.                 |
|         `pre`        |                             The number of `pre` tags.                            |
|      `sentences`     |                             The number of sentences.                             |
|      `syllables`     |                             The number of syllables.                             |
|        `words`       |                               The number of words.                               |

Since the pre-defined variables are calculated using the entire document, all `metric`-based rules are [`summary`-scoped](/topics/scopes.md).

## [Operators](#operators)

In addition to using the variables listed above, a `formula` may also use the following operators:

|    Operator    |      Description      |
| :------------: | :-------------------: |
|       `+`      |        Addition       |
|       `-`      |      Subtraction      |
|       `*`      |     Multiplication    |
|       `/`      |        Division       |
| `math.sqrt(x)` |   Square root of `x`  |
|  `math.abs(x)` | Absolute value of `x` |

A `condition` may use one of `>`, `<`, `==`, `>=`, and `<=`.

## [message](#message)

The result of a `formula` will be compared to its `condition` and inserted into its `message` format specifier (`%s`).

[capitalization](/checks/capitalization.md) [spelling](/checks/spelling.md)


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.vale.sh/checks/metric.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.