Shopify Checkout UI Extensions

Before writing code

Fetch live docs:

1. Fetch https://shopify.dev/docs/apps/build/checkout for checkout extensions
2. Web-search site:shopify.dev checkout ui extension targets for available targets
3. Web-search site:shopify.dev checkout ui components for UI primitives

What Are Checkout UI Extensions

Client-side extensions that add UI to Shopify's checkout:

• Render at specific extension targets (locations in checkout flow)
• Use Shopify's UI primitives (not Polaris, not HTML)
• Built with Preact and Remote DOM — sandboxed rendering
• Access checkout state via APIs (no direct DOM access)

Important: You cannot replace Shopify's checkout — only extend it at designated points.

Extension Targets

Locations where extensions can render:

Checkout Page

• purchase.checkout.block.render — general block in checkout
• purchase.checkout.header.render-after — after checkout header
• purchase.checkout.footer.render-after — after checkout footer
• purchase.checkout.contact.render-after — after contact info
• purchase.checkout.shipping-option-list.render-after — after shipping options
• purchase.checkout.payment-method-list.render-after — after payment methods
• purchase.checkout.actions.render-before — before pay button

Thank You Page

• purchase.thank-you.block.render — block on thank-you page

Order Status Page

• customer-account.order-status.block.render — block on order status

Post-Purchase

• purchase.post-purchase.render — full-page post-purchase upsell
• purchase.post-purchase.should-render — decide whether to show post-purchase

UI Primitives

Checkout extensions use Shopify's UI components (NOT Polaris, NOT HTML):

Extension Structure

extensions/checkout-ui/
├── src/
│   └── Checkout.tsx           # Extension component
├── shopify.extension.toml     # Configuration
├── locales/
│   └── en.default.json        # Translations
└── package.json

Configuration

api_version = "2025-01"

[[extensions]]
name = "Custom Checkout Banner"
handle = "custom-checkout-banner"
type = "ui_extension"

  [[extensions.targeting]]
  module = "./src/Checkout.tsx"
  target = "purchase.checkout.block.render"

Extension Component

import {
  Banner,
  useExtensionApi,
  useCartLines,
  useApplyCartLinesChange,
  reactExtension,
} from '@shopify/ui-extensions-react/checkout';

export default reactExtension(
  'purchase.checkout.block.render',
  () => <CheckoutBanner />,
);

function CheckoutBanner() {
  const { extension } = useExtensionApi();
  const cartLines = useCartLines();
  const applyCartLinesChange = useApplyCartLinesChange();

  const itemCount = cartLines.reduce((sum, line) => sum + line.quantity, 0);

  if (itemCount < 3) {
    return (
      <Banner status="info">
        Add {3 - itemCount} more item(s) for free shipping!
      </Banner>
    );
  }

  return null;
}

Checkout APIs (Hooks)

Best Practices

• Use Shopify UI primitives — never attempt raw HTML or Polaris components
• Keep checkout extensions minimal — do not slow down checkout
• Use useBuyerJourney() to validate before checkout progression
• Store extension configuration in metafields
• Support localization with locale files
• Test with shopify app dev and a development store checkout
• Follow Shopify's checkout UX guidelines — do not distract from payment

Fetch the Shopify checkout UI extensions docs for exact component APIs, available hooks, and extension target names before implementing.