# Resource tags in AWS Global Networks for Transit Gateways
Resource tags

A *tag* is a metadata label that either you or AWS assigns to an AWS resource. Each tag consists of a *key* and a *value*. For tags that you assign, you define the key and the value. For example, you might define the key as `purpose` and the value as `test` for one resource.

Tags help you do the following:
+ Identify and organize your AWS resources. Many AWS services support tagging, so you can assign the same tag to resources from different services to indicate that the resources are related.
+ Control access to your AWS resources. For more information, see [Controlling access to AWS resources using tags](https://docs.aws.amazon.com/IAM/latest/UserGuide/access_tags.html) in the *IAM User Guide*.

## Supported resources


The following global networks resources support tagging:
+ Global networks
+ Devices
+ Sites
+ Links

## Tagging restrictions


The following basic restrictions apply to tags on global networks resources:
+ Maximum number of tags that you can assign to a resource: 200
+ 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 the following characters: \$1 . : / = \$1 - and @
+ Keys and values are case sensitive
+ You cannot use `aws:` as a prefix for keys; it's reserved for AWS use