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# Tags Basics

### Tags Basics

Tags and Tagging

Tagging is a method of marking schema with a metadata object known as a Tag to make schema easier to find or link to. By using [List Tagged Schema](/en/docs/schema/v3/reference/http/tags-getresourcesbytags-GET/) you can retrieve all schema associated with a specific Tag.

A single schema can be associated with multiple Tags. Similarly, a single Tag can be associated with multiple schemas at a high level. So, Tags give you a flexible way of classifying schema.

One of the marquees uses of Tags is the Forge Schema Repository. Tags make schema discoverable by listing schema under the categories that they are tagged. Some Tags define categories that the schema belongs to, while others define what filters they react to.

Tag Collections and Tag Categories

A Tag Collection is a framework to store and manipulate a group of Tags. You can have only one Tag Collection per library, per group and one Tag Collection per organization. Only users or services with GROUP_ADMIN privileges can create Tag Collections.

A schema can only be associated with Tags that belong to the Tag Collection of the library, group, or compaorganization that the schema belongs to. You must be at least a SCHEMA_AUTHOR to associate Tags to a schema.

Within a Tag Collection, Tags can be grouped by category. Only Users or services with admin privileges can create Tag Categories. They can also assign Tags to Tag Categories. When you create a Tag Collection, a hidden Tag Category known as the default category is also created. Tags that have not been explicitly assigned to a Category are automatically assigned to the "default" category.

## The userData Object

Tags and Tag Category objects contain an attribute named `userData`.  This is an object to hold custom data relating to a Tag or Tag Category. It can hold any key-value pair. The only validation that the system performs on this object is to make sure that it is a valid JSON object.

In the Forge Schema Repository project, the `userData` object is used to hold metadata about each Tag that contains schema.