To update a tag, you must create an update spec for the tag. In the update spec, you set values for the fields to be changed, and omit values for the other fields. When you do an update operation using the update spec, only the fields that contain values are changed.

For example, you might use a timestamp in a tag description to identify a resource's last reconfiguration. After reconfiguring the resource, you update the tag description to contain the current time.