# Tagging restrictions
<a name="tag-restrictions"></a>

The following basic restrictions apply to tags on Amazon Braket resources:
+ Maximum number of tags that you can assign to a resource: 50
+ Maximum key length: 128 Unicode characters
+ Maximum value length: 256 Unicode characters
+ Valid characters for key and value: `a-z, A-Z, 0-9, space`, and these characters: `_ . : / = + -` and `@` 
+ Keys and values are case sensitive.
+ Don't use `aws` as a prefix for keys; it's reserved for AWS use.