# Cloud, Tags

Amazon S3 allows for tags to be included with uploaded/updated objects. Refer to their [documentation](https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-tagging.html) for details and restrictions. As these kinds of restrictions are often changed, and tagging may be expanded to other cloud services in future releases, SyncBackPro does not make any attempt to validate the tags you use. You can use [variables](Variables.md) both in the key name and the value name.

For reference, at the time of writing, these are the Amazon S3 object tagging restrictions:

- You can associate up to 10 tags with an object. Tags that are associated with an object must have unique tag keys.
- A tag key can be up to 128 Unicode characters in length, and tag values can be up to 256 Unicode characters in length.

- The key and values are case sensitive.
- The allowed characters across services are: letters, numbers, and spaces representable in UTF-8, and the following characters: + - = . _ : / @
- The **aws:** prefix is reserved for AWS use.

Note that the tags are only set on objects that are uploaded or updated. If you change the tags then they are only changed for existing objects if that object is updated.

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