Shopify Checkout Extensions

Overview

Shopify Checkout Extensions allow apps to render custom UI blocks inside Shopify's checkout without forking the checkout template. Shopify Functions let you replace backend logic — discounts, shipping, payment methods, and order validation — with custom WebAssembly modules that run inside Shopify's infrastructure. Together they replace the deprecated checkout.liquid customization approach and work with both Shopify Plus and non-Plus stores (UI extensions) or Plus-only (some Functions targets).

When to Use This Skill

• When adding custom UI blocks to checkout (upsells, trust badges, gift message fields, warranty options)
• When implementing custom discount logic beyond native Shopify discount rules (e.g., tiered discounts, B2B pricing)
• When creating custom shipping method filtering or renaming based on cart contents
• When building payment customization to hide/rename payment methods for specific customers
• When validating order contents before checkout completes (e.g., quantity limits, region restrictions)
• When replacing deprecated checkout.liquid customizations for Shopify Plus stores

Core Instructions

1. Scaffold an extension with Shopify CLI