> 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/0001-to-0023/aur0023.md).

# AUR0023

Resource key '{{0}}' has already been registered.

### **Error message**

Resource key '{{0}}' has already been registered.

### **Parameters**

Resource key (string)

### Error explanation

This error occurs when you attempt to register a resource (such as a custom element, attribute, value converter, or binding behavior) with a key that has already been registered in the container. Resource keys must be unique within a container.

### Common causes

* Attempting to register the same resource more than once.
* Using the same name for multiple resources of the same type.
* A plugin or library is registering a resource with a name that conflicts with one in your application.

### How to fix

* Use unique names for your resources (elements, attributes, value converters, binding behaviors, etc.).
* Check for duplicate registrations in your code and in any plugins you are using.
* If a plugin is causing the conflict, consult its documentation or consider renaming your resource.

### Debugging tips

* Check the stack trace to see where the duplicate registration is occurring.
* Search your codebase for all registrations of the resource key in question.
* If using plugins, try disabling them one at a time to isolate the source.


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