Shopify Metafields: The Feature Most Store Owners Don't Know Exists Metafields are Shopify's secret weapon. They let you add custom data to products, collections, and pages that don't fit standard fields. Size guides per product category. Ingredient lists. Compatibility charts. Care instructions. Before metafields, you'd need custom code or an app. Now you define them in settings, populate them per product, and display them in your theme. Stop paying for apps that do what metafields do for free.