# Tag
<a name="API_control_Tag"></a>

 A key-value pair that you use to label your resources. You can add tags to new resources when you create them, or you can add tags to existing resources. Tags can help you organize, track costs for, and control access to resources. 

## Contents
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 ** Key **   <a name="AmazonS3-Type-control_Tag-Key"></a>
The key of the key-value pair of a tag added to your Amazon resource. A tag key can be up to 128 Unicode characters in length and is case-sensitive. System created tags that begin with `aws:` aren’t supported.   
Type: String  
Length Constraints: Minimum length of 1. Maximum length of 128.  
Pattern: `^([\p{L}\p{Z}\p{N}_.:/=+\-@]*)$`   
Required: Yes

 ** Value **   <a name="AmazonS3-Type-control_Tag-Value"></a>
 The value of the key-value pair of a tag added to your Amazon resource. A tag value can be up to 256 Unicode characters in length and is case-sensitive.   
Type: String  
Length Constraints: Minimum length of 0. Maximum length of 256.  
Pattern: `^([\p{L}\p{Z}\p{N}_.:/=+\-@]*)$`   
Required: Yes

## See Also
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For more information about using this API in one of the language-specific Amazon SDKs, see the following:
+  [Amazon SDK for C\$1\$1](https://docs.amazonaws.cn/goto/SdkForCpp/s3control-2018-08-20/Tag) 
+  [Amazon SDK for Java V2](https://docs.amazonaws.cn/goto/SdkForJavaV2/s3control-2018-08-20/Tag) 
+  [Amazon SDK for Ruby V3](https://docs.amazonaws.cn/goto/SdkForRubyV3/s3control-2018-08-20/Tag)