> 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/0088-to-0723/aur0089.md).

# AUR0089

Attribute pattern "yyyy" has already been registered.

### **Error message**

Attribute pattern "{{0}}" has already been registered.

### **Parameters**

1. `pattern`: The duplicate pattern string that was attempted to be registered.

### Error explanation

This error occurs when you attempt to register an attribute pattern string with the `IAttributeParser` that has already been registered. Each pattern string must be unique.

### Common causes

* Defining the same pattern string in multiple `@attributePattern` decorators or calls to `IAttributeParser.registerPattern`.
* Accidentally providing the same `AttributePatternDefinition` object multiple times during registration.
* A plugin or library registering a pattern that conflicts with one already defined in your application or another plugin.

### How to fix

* Ensure each attribute pattern string defined in your application and plugins is unique.
* Check for duplicate pattern definitions in your codebase.
* If a conflict exists with a third-party plugin, consider renaming your pattern or contacting the plugin author.

### Debugging tips

* Identify the duplicate pattern string from the error message.
* Search your codebase and dependencies for where this pattern string is defined and registered.
* Temporarily remove or comment out pattern registrations to isolate the source of the duplication.


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