---
title: Fields
slug: web-experimentation/docs/fields
docTags: 
createdAt: 2026-07-23T11:40:26.165Z
---

When you create an experience template in Optimizely Web Experimentation and Optimizely Personalization, the Template Builder opens with the option for you to add **Editable Fields**. Each field defines a property that users can customize on the template. For example, on a pop-up, you can provide fields to customize the message, call to action, width and height, and timing of when it should display.

Each field requires an API name, which you can use to reference the field in HTML. For example, if you create a field with the API name *height*, you can reference it in HTML as `{{ extension.height }}` or in JS as `extension.height`. The **Label** is a human-readable name like "Pop-up Height", and you can add an optional **Default Value** like `400`.

You can use the fields and define their behavior by using the top code boxes.

![](https://api.archbee.com/api/optimize/BrbvVORKJ5iIeSMZye5kI/MeC_NCw5yxGMwM-SQSa5l_32f34e84d638b3449969aa1798ce3b195df83f7cf245760f7bf4f8a199e120a9-image.png)