Shopify Metafields for AI Agents: Implementation Reference (2026)

The two namespaces that matter

1. Shopify Standard Product Taxonomy (custom.shopify.*)

Shopify's Standard Product Taxonomy is a hierarchical product classification system (similar to Google's product taxonomy) that Shopify introduced in 2023. When you set a product's Product category in Shopify Admin, Shopify assigns the product to a node in the taxonomy tree and makes the taxonomy attributes available as pre-defined metafields.

These metafields appear in Admin under a product's Specifications section (for taxonomy-enabled categories). They sync to Google Merchant Center automatically via the Google & YouTube app, mapping to the equivalent Google product attributes. Setting them is the most efficient path to populating Merchant Center attributes — you fill them once in Shopify and they flow to Google without a separate feed file.

2. Google Shopping namespace (mm-google-shopping.*)

The Google Shopping namespace is a set of metafield definitions installed by the Google & YouTube app. These metafields map 1:1 to Google Merchant Center feed attributes. If the Standard Taxonomy doesn't cover a field you need (for example, identifier_exists for GTIN-exempt products, or custom_label_0 for campaign segmentation), you add it here.

Key difference: Standard Taxonomy metafields appear in the product form under "Specifications." Google Shopping metafields appear under "Metafields" at the bottom of the product editor. Both sync to Merchant Center; they're just different entry points.

The 8 metafields — reference table

Note: GTIN is not a metafield — it is the Barcode field on each product variant. It is listed here because it is the most impactful signal and is often confused with a metafield.

Creating metafields in Shopify Admin

Method 1: Admin UI (single product)

1. In Shopify Admin, go to Settings → Custom data → Products
2. Click Add definition. Set namespace and key exactly as listed in the table above (e.g., namespace: mm-google-shopping, key: mpn). Set type to Single line text.
3. Save the definition. The field now appears in the product editor under "Metafields."
4. On each product, scroll to the Metafields section and fill in the value.

The Google & YouTube app creates mm-google-shopping.* definitions automatically when you install it — you may already have these definitions and just need to populate values.

Method 2: Admin API (bulk update via script)

For catalogs with 50+ products, use the Shopify Admin API's POST /admin/api/2024-01/products/{product_id}/metafields.json endpoint. Below is the payload format for a single metafield:

POST /admin/api/2024-01/products/123456789/metafields.json

{
  "metafield": {
    "namespace": "mm-google-shopping",
    "key": "mpn",
    "value": "ACME-WB-100-BLK",
    "type": "single_line_text"
  }
}

For bulk updates, export your product CSV (Admin → Products → Export), add columns for each metafield value, then write a script to call the API per product. The Shopify Node.js or Python SDK makes this straightforward — see the metafields blog post for a working bulk script example.

Method 3: CSV import (metafield columns)

Shopify's product CSV import supports metafield columns in the format Metafield: namespace.key [type]. Export your current products to CSV, add columns for the metafields you want to populate, fill values, and re-import with "Overwrite existing products." Example column header:

Metafield: mm-google-shopping.mpn [single_line_text]

This method is the fastest for non-technical merchants doing a one-time bulk populate.

Mapping metafields to Product JSON-LD via Liquid

The Google & YouTube app handles Merchant Center sync. But for Product JSON-LD on your product pages (used by ChatGPT Shopping, Perplexity, and Bing Shopping), you need to output these values in your theme's JSON-LD Liquid template. Most Shopify themes do not include metafield values in their JSON-LD output by default.

Add these Liquid conditionals to your theme's JSON-LD block (typically in sections/product-template.liquid or a dedicated snippets/product-schema.liquid file):

{% comment %} Inside the Product JSON-LD script block {% endcomment %}
{
  "@type": "Product",
  "name": {{ product.title | json }},
  "description": {{ product.description | strip_html | json }},
  "brand": {
    "@type": "Brand",
    "name": {{ product.vendor | json }}
  },
  "offers": {
    "@type": "Offer",
    "price": {{ current_variant.price | money_without_currency | json }},
    "priceCurrency": {{ shop.currency | json }},
    "availability": "{% if current_variant.available %}https://schema.org/InStock{% else %}https://schema.org/OutOfStock{% endif %}"
    {% if current_variant.barcode != blank %}
    ,"gtin13": {{ current_variant.barcode | json }}
    {% endif %}
  }
  {% assign mpn = product.metafields['mm-google-shopping']['mpn'] %}
  {% if mpn != blank %}
  ,"mpn": {{ mpn.value | json }}
  {% endif %}
  {% assign material = product.metafields['shopify']['material-2'] %}
  {% if material != blank %}
  ,"material": {{ material.value | json }}
  {% endif %}
}

Bulk management tools

For ongoing metafield maintenance at catalog scale, these third-party apps in the Shopify App Store handle bulk edits without API scripting:

• Metafields Guru — bulk export/import of metafields to CSV, field definitions, and support for all metafield types.
• Bulk Product Editor by Hextom — bulk edits across products, variants, and metafields with filtering by collection or tag.
• Shopify Flow (for automation) — create workflows that populate metafields when products are created or tagged, useful for maintaining metafield consistency as new products are added.