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Restrictions on tagging AWS VMs and CloudFormation stacks

Restrictions on tagging AWS VMs and CloudFormation stacks

CloudFormation Administrators must follow the Amazon guidelines when defining a tag to assign metadata to a VM or CloudFormation stack.

  • Maximum key length: 127 Unicode characters
  • Maximum value length: 255 Unicode characters
  • Maximum number of tags per resource: 10
  • Do not assign the reserved prefix aws:

    AWS-assigned tag names and values are assigned the aws: prefix. AWS-assigned tag names do not count toward the tag limit of 10. User-assigned tag names have the user: prefix 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, the request is rejected.
  • You cannot tag a resource at the same time as you create it. Tagging requires a separate action after the resource is created.
  • You cannot backdate the application of a tag.
  • Allowed characters are letters, whitespace, and numbers representable in UTF-8, plus the following special characters: + - = . _ : /

    To use characters outside this set, encode the tag using standard base-64.

    For information on tag restrictions, see the Amazon Web Services documentation at

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