What are all Tag Restrictions for AWS services by Raj Gupta

The following basic restrictions apply to tags for any AWS services:

• Maximum number of tags per resource – 50
• For each resource, each tag key must be unique, and each tag key can have only one value.
• Maximum key length – 128 Unicode characters in UTF-8
• Maximum value length – 256 Unicode characters in UTF-8
• Although EC2 allows for any character in its tags, other services may be more restrictive. Generally allowed characters are: letters, numbers, and spaces re-presentable in UTF-8, and the following characters: + - = . _ : / @. These characters may not be allowed by more restrictive services.
• Tag keys and values are case-sensitive.
• Don't use the aws: prefix for either keys or values; it's reserved for AWS use. You can't edit or delete tag keys or values with this prefix. Tags with this prefix do not count against your tags per resource limit.
• You can tag public or shared resources, but the tags you assign are available only to your AWS account and not to the other accounts sharing the resource.
• You can't tag all resources.