> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abbyy.com/llms.txt
> Use this file to discover all available pages before exploring further.

# RuleError

> Document skill validation rule error.

`RuleError` describes a single Document skill validation rule error returned by [`Document.RuleErrors`](/vantage/documentation/skill-designer/process/custom-activity/document).

## Properties

| Name              | Type   | Access    | Description                                                                                                                 |
| :---------------- | :----- | :-------- | :-------------------------------------------------------------------------------------------------------------------------- |
| **CustomMessage** | string | Read-only | The custom error message from a custom skill. Returns an empty string for built-in rules, or when no custom message is set. |
| **ErrorType**     | string | Read-only | The error type. Returned only for built-in rules.                                                                           |

## Related topics

<CardGroup cols={2}>
  <Card title="Document" icon="file-lines" href="/vantage/documentation/skill-designer/process/custom-activity/document">
    The document currently being processed by the Custom activity.
  </Card>

  <Card title="Object model" icon="diagram-project" href="/vantage/documentation/skill-designer/process/custom-activity/object-model">
    Full JavaScript object reference for Custom activity scripts.
  </Card>
</CardGroup>