Shopify line item properties — the complete 2026 guide

What are Shopify line item properties?

Line item properties are per-order customer input attached to a specific cart line. They store things like engraving text, uploaded photo URLs, monogram initials, gift messages, and dates. They don't create variants, don't affect inventory, and travel with the order through checkout, admin, POS, email confirmations, and fulfillment.

You add them via the properties[Field Name] input on the product form (theme code) or via a product options app like Print It My Way (much more flexible).

Step-by-step setup

1. Understand what line-item properties are. Per-order customer input. Not variants. Not metafields.
2. Add via app or theme code. App = flexible. Theme code = free but limited.
3. Test cart + order + email display. Properties should appear in all three.
4. Verify GraphQL customAttributes on Storefront API. Line-item properties map to customAttributes in the Storefront GraphQL schema.

How they're structured

Each line-item property is a key-value pair. Key = the field name (e.g. "Engraving text"). Value = the customer's input (e.g. "Sarah").

They live on the line_item.properties array of the order. Example order line:

{
  "line_items": [{
    "title": "Custom Mug",
    "variant_title": "White / 11oz",
    "properties": [
      { "name": "Engraving text", "value": "Sarah" },
      { "name": "Font", "value": "Playfair Display" },
      { "name": "_hidden_setup_fee", "value": "5.00" }
    ]
  }]
}

How to add via app

Install Print It My Way. Add fields to your product's personalizer. Customer input becomes line-item properties automatically. No theme editing.

How to add via theme code (no app)

Add this to product-form.liquid:

<label>Engraving text</label>
<input type="text" name="properties[Engraving text]" maxlength="20">

Cheap and works, but no validation, preview, mobile UI, or per-field pricing.

Hidden properties (underscore prefix)

A line-item property whose key starts with an underscore is hidden from customer-facing displays (cart, checkout, order confirmation email) but still stored in the order.

<input type="hidden" name="properties[_setup_fee]" value="5.00">

Use for internal fulfillment metadata — routing tags, batch codes, print-file URLs.

GraphQL and customAttributes

On the Storefront API GraphQL schema, line-item properties are exposed as customAttributes on the CartLine type:

cart {
  lines(first: 10) {
    edges {
      node {
        merchandise { ... }
        attributes {
          key
          value
        }
      }
    }
  }
}

Character and count limits

• Key length — 100 characters
• Value length — 255 characters (per property). Longer values need a hidden URL to a stored file.
• Properties per line item — practically unlimited (Shopify doesn't cap; slowdown starts around 50+).

How POD partners consume them

Printful, Printify, Gelato all read line-item properties from the order via their standard integration. Custom text becomes engraved text. Uploaded photo URLs become print files. No manual transfer needed.

Frequently asked questions