# Managing Service Quotas resources with tags
<a name="sq-tagging"></a>

You can use tags to categorize resources by purpose, owner, environment, or other criteria. A *tag* is a custom attribute label that you add to an Amazon resource to make it easier to identify, organize, and search for resources. Each tag includes two parts: 
+ A **tag key**, such as `CostCenter`, `Environment`, or `Project`. Tag keys are case sensitive.
+ A **tag value**, such as `111122223333` or `Production`. You can set the value of a tag to an empty string, but you can't set the value of a tag to null. Omitting the tag value is the same as using an empty string. Like tag keys, tag values are case sensitive.

Tags help you do the following:
+ Identify and organize your Amazon resources. Many services support tagging, so you can assign the same tag to resources from different services to indicate that the resources are related.
+ Track your Amazon costs. You activate these tags on the Amazon Billing and Cost Management dashboard. Amazon uses the tags to categorize your costs and deliver a monthly cost allocation report to you. For more information, see [Use cost allocation tags](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/cost-alloc-tags.html) in the [Amazon Billing User Guide](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/).
+ Control access to your Amazon resources. For more information, see [Controlling access using tags](https://docs.amazonaws.cn/IAM/latest/UserGuide/access_tags.html) in the * [IAM User Guide](https://docs.amazonaws.cn/IAM/latest/UserGuide/)*. 

**Topics**
+ [Service Quotas resources that support tagging](#sq-supported-resources)
+ [Tag restrictions](#sq-tagging-restrictions)
+ [Enabling the required permissions for tagging Service Quotas resources](sq_tags_permissions.md)
+ [Managing Service Quotas tags](sq_tags_managing-console.md)
+ [Controlling access using Service Quotas tags](sq_tags_access.md)

## Service Quotas resources that support tagging
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Service Quotas supports tagging the **Applied quotas** resource. An applied quota is a quota that you requested an increase for, *and* the increase was approved by Amazon Web Services Support.

**Important**  
You can only tag quotas if they have an applied quota value. Quotas with default quota values cannot be tagged.  
Do not store personally identifiable information (PII) or other confidential or sensitive information in tags. Tags are not intended to be used for private or sensitive data.

## Tag restrictions
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Restrictions apply to tags on Service Quotas resources, including:
+ Maximum number of tags that you can assign to a resource – 50 
+ Maximum tag key length – 128 Unicode characters 
+ Maximum tag value length – 256 Unicode characters 
+ Valid characters for tag key and value – a-z, A-Z, 0-9, space, and the following characters: \$1 . : / = \$1 - and @
+ Tag keys and values are case sensitive.
+ Don't use `aws:` as a prefix for tag keys. It is reserved for Amazon use.