---
title: "Shopify cart transform function, verified November 2026"
description: "What a Shopify cart transform's price looks like in a real Storefront cart: the line's own price changes with no discount allocation, a function that returns nothing leaves no trace, and discount codes are taken from the new price. Verified 3 November 2026 on Shopify's 2026-10 API."
url: https://offersuite.io/shopify/cart-transform
updated: 2026-11-03
---

# A Shopify cart transform in a real cart

A cart transform is a function an app registers on a store. Shopify runs it each time a cart is priced, and it can change what a line is: its price, its title, or the lines it is made of. These carts show a price it set, read through the Storefront API.

Verified 3 November 2026 on Shopify’s 2026-10 API, in carts built on a real store. Each statement marked with a tick is checked against the cart Shopify returned.

## The transform's price becomes the line's own price

The function behind these carts belongs to an app's cart transform. It reads a cart attribute to decide what to do; given one, it returns an update operation that sets a fixed price per unit on a cart line.

The cart reports that price as the line's price. Nothing marks it as changed: the variant still costs $40.00 in the catalog, and the cart line reads $34.00. Shopify runs an update operation only on Shopify Plus stores and development stores; this store is both.

The operation the function returns for this cart

```
{
  "operations": [
    {
      "lineUpdate": {
        "cartLineId": "gid://shopify/CartLine/…",
        "price": {
          "adjustment": { "fixedPricePerUnit": { "amount": "34.00" } }
        }
      }
    }
  ]
}
```

**A cart transform prices one line** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- The cart attribute the app's cart transform reads

#### What Shopify returned

The cart Shopify returned: A cart transform prices one line

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $34.00 | none | $34.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $34.00 |  |  |  |

#### What that shows

- The line's price read $34.00, not the variant's $40.00, and the cart's subtotal and total were $34.00.
- No discount allocation appeared anywhere in the cart, and no warning: the $6.00 is not reported as a discount.

## A transform's price is not a discount

The same product on the same store can be priced by a discount function instead. That saving comes back as an allocation on the line, under the discount's title, and the line's price before discounts stays at the variant's.

The transform's saving is in no list. A buy box that builds its strikethrough from the cart's discount allocations has nothing to show for the line above, and one that reads the line's price shows $34.00 as if it were the catalog price.

**A discount function prices one line** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- The cart attribute the app discount's function reads

#### What Shopify returned

The cart Shopify returned: A discount function prices one line

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $40.00 | −$10.00 automatic, “Offer Suite” | $30.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $30.00 |  |  |  |

#### What that shows

- The $40.00 line cost $30.00.
- The line carried one automatic discount allocation of $10.00, named by the discount's title.
- The cart's own list of discount allocations was empty: a product discount is reported on its line only.

## Without the attribute, the transform leaves no trace

The transform is still registered on the store and its function still runs on this cart. It finds no attribute and returns an empty list of operations.

The cart reads as it would on a store with no cart transform at all.

**A cart transform that returns no operations** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- No cart attribute, so the app's functions return no operations

#### What Shopify returned

The cart Shopify returned: A cart transform that returns no operations

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $40.00 | none | $40.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $40.00 |  |  |  |

#### What that shows

- The line's price was the variant's $40.00, and so was the cart total.
- Nothing in the cart says a cart transform ran: no allocation and no warning.

## An update acts on a whole line

An update operation names a cart line, not a quantity of it. This function prices one unit, so for a line of two it returns no operation, and both units stay at the variant's price in one line.

A discount behaves differently. A discount candidate can target one unit of a line, and Shopify then splits the line in two, as the second cart shows.

**A line of two, and a transform that prices one unit** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 2 × Single Bag at $40.00, bought once
- The cart attribute the app's cart transform reads

#### What Shopify returned

The cart Shopify returned: A line of two, and a transform that prices one unit

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 2 | $40.00 | none | $80.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $80.00 |  |  |  |

#### What that shows

- The cart came back as one line of quantity 2: it was not split.
- Both units were at the variant's $40.00, a cart total of $80.00, with no allocation and no warning.

**A function discounts one unit of a line of two** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 2 × Single Bag at $40.00, bought once
- The cart attribute the app discount's function reads

#### What Shopify returned

The cart Shopify returned: A function discounts one unit of a line of two

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $40.00 | none | $40.00 |
| Single Bag | 1 | $40.00 | −$10.00 automatic, “Offer Suite” | $30.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $70.00 |  |  |  |

#### What that shows

- One line of quantity 2 went in; the cart came back with two lines of quantity 1.
- One of them cost $30.00 with the $10.00 allocation, the other $40.00 with none.
- The cart total was $70.00.

## Discount codes are taken from the transform's price

To a discount, the transform's price is the price. An order code's percentage was taken from $34.00, so a margin forecast for a buyer with a code starts from the transform's price.

A product code on the same line applied as well. Two product discounts on one line do not stack; a transform's price and a product discount do, because only one of them is a discount.

**An order code on a line priced by a cart transform** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- The cart attribute the app's cart transform reads
- Code VERIFY-ORDER10: 10% off the order, one-time purchases only, combines with product and shipping discounts

#### What Shopify returned

The cart Shopify returned: An order code on a line priced by a cart transform

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $34.00 | none | $34.00 |
| Discounts on the cart | −$3.40 code VERIFY-ORDER10 |  |  |  |
| Cart total | $30.60 |  |  |  |

- `VERIFY-ORDER10` applicable: true

#### What that shows

- The code applied, and took 10% of the transform's $34.00, not of the variant's $40.00: $3.40.
- The cart total was $30.60. The line still read $34.00 and carried no allocation; the code's was in the cart's list.

**A product code on a line priced by a cart transform** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- The cart attribute the app's cart transform reads
- Code VERIFY-BAG5: $5.00 off the bag, one-time purchases only, combines with product, order and shipping discounts

#### What Shopify returned

The cart Shopify returned: A product code on a line priced by a cart transform

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $34.00 | −$5.00 code VERIFY-BAG5 | $29.00 |
| Discounts on the cart | none |  |  |  |
| Cart total | $29.00 |  |  |  |

- `VERIFY-BAG5` applicable: true

#### What that shows

- The code applied on the line: $5.00 off the transform's $34.00, a line total and a cart total of $29.00.
- The line's price before discounts read $34.00, and the code's allocation was the only one in the cart.

## The delivery rates are the store's own

A price set by a transform changes merchandise. With a delivery address, this cart was quoted the rates the store quotes for the same product at its catalog price, and nothing discounted them.

**A line priced by a cart transform, with a delivery address** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- The cart attribute the app's cart transform reads
- A US delivery address, with the cheapest rate selected

#### What Shopify returned

The cart Shopify returned: A line priced by a cart transform, with a delivery address

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $34.00 | none | $34.00 |
| Discounts on the cart | none |  |  |  |
| Delivery: Standard selected Quoted: Standard $8.00, Express $15.00 | none | $8.00 |  |  |
| Cart total | $42.00 |  |  |  |

#### What that shows

- The store quoted Standard at $8.00 and Express at $15.00, and no discount was allocated to the rate or anywhere else in the cart.
- With Standard selected the cart total was $42.00: the $34.00 line and the $8.00 rate.

**The same cart with no discount** Verified 3 November 2026 · API 2026-10

#### Into the cart

- 1 × Single Bag at $40.00, bought once
- No cart attribute, so the app's functions return no operations
- A US delivery address, with the cheapest rate selected

#### What Shopify returned

The cart Shopify returned: The same cart with no discount

| Line | Quantity | Price | Discounts on the line | Line total |
| --- | --- | --- | --- | --- |
| Single Bag | 1 | $40.00 | none | $40.00 |
| Discounts on the cart | none |  |  |  |
| Delivery: Standard selected Quoted: Standard $8.00, Express $15.00 | none | $8.00 |  |  |
| Cart total | $48.00 |  |  |  |

#### What that shows

- The store quoted Standard at $8.00 and Express at $15.00; with Standard selected the cart total was $48.00.

## How this was verified

Every cart on this page was built through the Storefront API on a Shopify Plus development store we keep for this, on API version 2026-10, and read back as Shopify priced it. The store sells one product in these carts: Single Bag, at $40.00, also sold on a selling plan named “Every 30 days” that has no pricing policy. It quotes two delivery rates to a US address.

It has one automatic app discount, titled “Offer Suite”, with a product class and a shipping class, set to combine with product, order and shipping discounts. Its function reads a cart attribute: with it, the function takes 25% off one unit of Single Bag bought once, or $8.00 off the unit on its selling plan, and makes the cheapest delivery rate free. Without it, the function returns no operations.

The same app has a cart transform registered on the store. Its function reads a cart attribute of the same kind: with it, the function sets the price of one unit of Single Bag bought once to $34.00. Without it, or for a line of more than one unit, the function returns no operations.

The other discounts in these carts, as they are set on the store

| Discount | Class | Gives | Combination setting |
| --- | --- | --- | --- |
| Code VERIFY-ORDER10 | Order | 10% off the order, one-time purchases only | combines with product and shipping discounts |
| Code VERIFY-BAG5 | Product | $5.00 off the bag, one-time purchases only | combines with product, order and shipping discounts |

A suite builds these carts again and reads the discount settings from the store before it does. A statement that no longer matches the cart takes this page down until it is corrected, and no cart stands for more than 90 days without being built again. This is what one store returned on one API version: your store’s plan, markets and other apps can change the result, so build the cart.

Seen something different on your store? Write to [privacy@offersuite.io](mailto:privacy@offersuite.io) with the cart and we’ll run it.

## Related

- [Shopify, verified **Shopify offer mechanics, verified on a real store** How Shopify discounts, discount functions, cart transforms, selling plans, the Storefront cart and their limits behave, shown in real carts built on a Shopify store and built again at least every 90 days.](https://offersuite.io/shopify)
- [Feature **Publish and verify on a real Shopify cart** Publishing writes the offer to Shopify, builds a real cart for every visible option and goes live only if each one charges what the offer promises.](https://offersuite.io/features/publish-and-verify)
- [Feature **Serve a verified offer to your buy box** Show a verified offer through the Verified offer theme block, your developers' code on the public API, or your agent, with every price computed by the server.](https://offersuite.io/features/buy-box)
- [Shopify, verified **Shopify discount functions, verified November 2026** What a Shopify discount function's output looks like in a real Storefront cart: where the allocation lands, a line split by a partial discount, and one discount with a product and a shipping class. Verified 3 November 2026 on Shopify's 2026-10 API.](https://offersuite.io/shopify/discount-functions)
- [Shopify, verified **Shopify Storefront cart discounts, verified November 2026** Where a Shopify Storefront API cart reports each kind of discount: product discounts on the line, order discounts on the cart, shipping discounts on the delivery group, and codes it did not apply in warnings. Verified 3 November 2026 on Shopify's 2026-10 API.](https://offersuite.io/shopify/storefront-cart)
- [Shopify, verified **Two Shopify product discounts on one line, verified November 2026** Real carts with two Shopify product discounts aimed at one line: they did not stack even when both allowed product discounts, and a larger code that combines with nothing replaced the automatic discount. Verified 3 November 2026 on Shopify's 2026-10 API.](https://offersuite.io/shopify/discount-combinations/product-and-product)