> ## Documentation Index
> Fetch the complete documentation index at: https://docs.knitbundles.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Shopify integration

> How Knit runs on a Shopify Liquid storefront

On a standard Shopify Liquid theme, Knit uses three pieces:

| Piece                     | Role                                                |
| ------------------------- | --------------------------------------------------- |
| Theme app extension       | Renders the bundle widget on matching product pages |
| Cart line-item properties | Carries `__FB_ATC_UID` so lines stay grouped        |
| Discount Function         | Applies the bundle reward at checkout               |

Enable the Knit app embed in the theme editor so the widget can mount. You do **not** need the theme app extension for [headless endpoints](/headless-bundles-api) or [Tapcart](/tapcart). Those load from the Knit app origin:

```
https://app.knit-bundle.co
```

## Add to cart override

If a bundle has **ATC override** enabled, the shopper clicks the theme's Add to Cart button and Knit adds the bundle lines instead of a single product. The widget should not show its own add-to-cart button in that mode.

If override is off, the widget shows its own add-to-cart control.

## Checkout

The discount still comes from the Knit automatic discount in Shopify admin → **Discounts**. Details: [How discounts apply](/how-discounts-apply).