---
title: Define user attributes to build audiences in Feature Experimentation
slug: feature-experimentation/docs/define-user-attributes-to-build-audiences-in-feature-experimentation
docTags: 
createdAt: 2026-08-05T20:39:59.000Z
---

- Optimizely Feature Experimentation

Use attributes to build the [audiences](docId\:UDBvr5a8WHNkyOqzPhOr9) that see your experiments, and use the **Attributes** tab to manage your user attributes.

:::hint{type="info"}
**Note**

All attributes created in a project remain in the datafile.
:::

To create a new attribute key:

1. Go to **Audiences > Attributes**.
2. Click **Create New Attribute**.

   ![Create New Attribute](https://api.archbee.com/api/optimize/BrbvVORKJ5iIeSMZye5kI/vJxAqde57ZbgptRsHF4f--20260720-145741.png)
3. Enter a key for the attribute.
   - Attribute keys must be unique within your project. For example, an attribute for visitors in the United States might be called `US_VISITOR`. You can pass attributes to the Optimizely Feature Experimentation SDK in your code, so update your code with any changes to your keys.
4. Click **Save**.

:::hint{type="info"}
**Note**

Attribute keys must be unique

- within your project.
- across multiple projects, if you use the same user IDs across projects. Using identical attribute keys in multiple projects can cause incorrect segmentation on the [Results page](docId\:mrUblIuNVOZc1dvjWdsbw).
:::

## Attribute value formatting

You define attribute values in the **Audiences** tab, not the **Attributes** tab.

Attribute values are not explicitly typed in the Optimizely app. However, based on the format of the value you pass, you can choose different audience match criteria (comparison operations like `greater than` or `equal to`). For information, see [Target audiences](docId\:UDBvr5a8WHNkyOqzPhOr9).