Shopify discount functions in a real cart

The discount lands on the line the function targets

The function behind these carts belongs to an automatic app discount. It reads a cart attribute to decide what to do; given one, it returns a product discount candidate that targets a cart line.

The cart reports that discount on the line, as an automatic discount allocation that carries the discount's title. The function's candidate set no message of its own.

{
  "operations": [
    {
      "productDiscountsAdd": {
        "candidates": [
          {
            "targets": [{ "cartLine": { "id": "gid://shopify/CartLine/…" } }],
            "value": { "percentage": { "value": 25 } }
          }
        ],
        "selectionStrategy": "ALL"
      }
    }
  ]
}

A function that returns no operations leaves no trace

Without the attribute, the same function returns an empty list of operations. The discount is still active on the store and its function still runs.

Nothing in the cart says so. There is no allocation of zero, no warning and no list of discounts that were considered: a function that chose not to act and a discount that does not exist read the same from the cart.

A discount on part of a line splits the line

A candidate's cart line target may name a quantity. This function discounts one unit, so on a line of two it targets one of them.

Shopify did not return one line with an averaged price. It returned two lines, so code that finds a line by its variant and expects one match finds two.

{
  "targets": [{ "cartLine": { "id": "gid://shopify/CartLine/…", "quantity": 1 } }],
  "value": { "percentage": { "value": 25 } }
}

One discount can carry a product class and a shipping class

The discount on this store has both classes, so Shopify runs both of the function's targets: the one for cart lines and the one for delivery options. The delivery target returns a candidate for the cheapest rate, with a message.

The two halves are named differently in the cart. The second cart is the same purchase with no discount, to show what the rate costs.

{
  "operations": [
    {
      "deliveryDiscountsAdd": {
        "candidates": [
          {
            "message": "Free shipping",
            "targets": [{ "deliveryOption": { "handle": "…" } }],
            "value": { "percentage": { "value": 100 } }
          }
        ],
        "selectionStrategy": "ALL"
      }
    }
  ]
}

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.

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 with the cart and we’ll run it.