AWS Billing and Cost Management
User Guide (Version 2.0)

User-Defined Tag Restrictions

The following basic restrictions apply to tags:

  • The maximum key length is 128 Unicode characters.

  • The maximum value length is 256 Unicode characters.

  • Tags are case sensitive.

  • The maximum number of tags per resource is 50.

  • The maximum active tag keys for Billing and Cost Management reports is 500.

  • The reserved prefix is aws:.

    AWS generated tag names and values are automatically assigned the aws: prefix, which you can't assign. User-defined tag names have the prefix user: in the cost allocation report.

  • Use each key only once for each resource. If you attempt to use the same key twice on the same resource, your request will be rejected.

  • You can't tag a resource at the same time you create it. Tagging requires a separate action after the resource is created.

  • You can't backdate the application of a tag. This means that tags only start appearing on your cost allocation report after you apply them and don't appear on earlier reports.

  • Allowed characters are Unicode letters, whitespace, and numbers, plus the following special characters: + - = . _ : /


    If you need characters outside this allowed set, you can apply standard base-64 encoding to your tag. Billing and Cost Management does not encode or decode your tag for you.