> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/4100-to-4106/aur4105.md).

# AUR4105

## Error Message

`AUR4105: Unsupported rule {{ruleName}}`

## Description

This error occurs when attempting to hydrate a validation rule that is not recognized or supported by the current validation system. This can happen when:

1. Using custom rules that weren't registered
2. Deserializing rules from a different validation library
3. Rule names have changed between versions
4. Typos in rule names

## Common Scenarios

```typescript
// ❌ Problem: Unsupported rule name
const rules = [{
  property: 'age',
  rules: [{ name: 'isPositiveInteger' }] // Custom rule not registered
}];
```

## Solution

```typescript
// ✅ Correct: Register custom rules first
import { ValidationRules } from '@aurelia/validation';

// Register custom rule
ValidationRules.customRule(
  'isPositiveInteger',
  (value) => value > 0 && Number.isInteger(value),
  'Value must be a positive integer'
);

// Now the rule can be hydrated
validationRules.hydrateRules(rules);
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

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

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.aurelia.io/developer-guides/error-messages/4100-to-4106/aur4105.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

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.