# Tag Types

Tag functions have been upgraded on the platform. After the upgrade, a tag consists of a key and a value. Keys and values comply with the following rules:

- For the tags created after the upgrade, all characters in tags are automatically used as a key, and the value is empty. Tags consist of only digits, letters, hyphens (-), and underscores (_).
- For the tags that have been created before the upgrade:
  - If no period (.) is used in tags, all characters in tags are used as a key, and the value is empty.
  - If periods (.) are used in tags, the characters before the first period are used as a key and the characters after the first period are used as a value.

After the tag function upgrade, tag management APIs are classified as the APIs for 1D tags and the APIs for 2D tags.

- A 1D tag contains a string. All APIs for 1D tags are native OpenStack APIs. For details, see this section.
- A 2D tag consists of a key and a value. All APIs for 2D tags are ECS APIs. For details, see Tag Management.

- You are advised to use the APIs of the same type to add, delete, modify, or query tags.
- You are advised to use 2D tags.

Parent topic: Tag Management