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

A tag is a key-value pair. Allowed characters are letters, white space, and numbers that can be represented in UTF-8, and the following characters:` + - = . _ : /`.

## Contents
<a name="API_Tag_Contents"></a>

 ** Key **   <a name="efs-Type-Tag-Key"></a>
The tag key (String). The key can't start with `aws:`.  
Type: String  
Length Constraints: Minimum length of 1. Maximum length of 128.  
Pattern: `^(?![aA]{1}[wW]{1}[sS]{1}:)([\p{L}\p{Z}\p{N}_.:/=+\-@]+)$`   
Required: Yes

 ** Value **   <a name="efs-Type-Tag-Value"></a>
The value of the tag key.  
Type: String  
Length Constraints: 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 AWS SDKs, see the following:
+  [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/elasticfilesystem-2015-02-01/Tag) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/elasticfilesystem-2015-02-01/Tag) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/elasticfilesystem-2015-02-01/Tag)