Checkout Customization

When to use this skill

Use this skill when:

• Building checkout UI extensions
• Adding custom fields to checkout
• Implementing payment customizations
• Creating post-purchase upsells
• Extending customer account pages
• Customizing the checkout experience
• Adding custom validation logic

Overview

Checkout customization uses extensions that are:

• Upgrade-safe – Work with Shop Pay and new features
• Performant – Run in a sandboxed environment
• Secure – Limited access for security

Extension Types

Getting Started

1. Create Checkout Extension

# In an existing app
shopify app generate extension

# Select: Checkout UI

2. Extension Structure

extensions/
└── checkout-ui/
    ├── src/
    │   └── Checkout.jsx
    ├── locales/
    │   └── en.default.json
    └── shopify.extension.toml

3. Configuration

# shopify.extension.toml
api_version = "2025-01"

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

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

Checkout UI Extensions

Basic Extension

// src/Checkout.jsx
import {
  reactExtension,
  Banner,
  useApi,
  useTranslate,
} from "@shopify/ui-extensions-react/checkout";

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

function Extension() {
  const translate = useTranslate();

  return (
    <Banner title={translate("welcomeMessage")}>
      Thank you for shopping with us!
    </Banner>
  );
}

Extension Targets

Common checkout targets:

// Before shipping options
"purchase.checkout.shipping-option-list.render-before";

// After shipping options
"purchase.checkout.shipping-option-list.render-after";

// Payment method
"purchase.checkout.payment-method-list.render-before";

// Order summary
"purchase.checkout.cart-line-list.render-after";

// Static render (header/footer)
"purchase.checkout.header.render-after";
"purchase.checkout.footer.render-after";

// Block render (anywhere in checkout)
"purchase.checkout.block.render";

// Delivery address
"purchase.checkout.delivery-address.render-before";

Using Checkout Data

import {
  useCartLines,
  useTotalAmount,
  useShippingAddress,
  useBuyerJourney,
  useCustomer,
  useDiscountCodes,
} from "@shopify/ui-extensions-react/checkout";

function Extension() {
  const cartLines = useCartLines();
  const totalAmount = useTotalAmount();
  const shippingAddress = useShippingAddress();
  const customer = useCustomer();
  const discountCodes = useDiscountCodes();

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

  return (
    <BlockStack>
      <Text>Items in cart: {itemCount}</Text>
      <Text>Total: ${total}</Text>
      {customer && <Text>Welcome back, {customer.firstName}!</Text>}
    </BlockStack>
  );
}

UI Components

import {
  Banner,
  BlockStack,
  InlineStack,
  Text,
  Button,
  Checkbox,
  TextField,
  Select,
  Image,
  Divider,
  Heading,
  Link,
  View,
  Grid,
  Icon,
} from "@shopify/ui-extensions-react/checkout";

function Extension() {
  const [checked, setChecked] = useState(false);
  const [note, setNote] = useState("");

  return (
    <BlockStack spacing="base">
      <Heading level={2}>Gift Options</Heading>

      <Checkbox checked={checked} onChange={setChecked}>
        This is a gift
      </Checkbox>

      {checked && (
        <TextField
          label="Gift message"
          value={note}
          onChange={setNote}
          multiline
        />
      )}

      <InlineStack spacing="tight">
        <Button kind="secondary" onPress={() => {}}>
          Cancel
        </Button>
        <Button onPress={() => {}}>Save</Button>
      </InlineStack>
    </BlockStack>
  );
}

Custom Fields with Metafields

import {
  useApplyMetafieldsChange,
  useMetafield,
} from "@shopify/ui-extensions-react/checkout";

function GiftMessage() {
  const [message, setMessage] = useState("");
  const applyMetafieldsChange = useApplyMetafieldsChange();

  const handleChange = async (value) => {
    setMessage(value);
    await applyMetafieldsChange({
      type: "updateMetafield",
      namespace: "custom",
      key: "gift_message",
      valueType: "string",
      value,
    });
  };

  return (
    <TextField label="Gift message" value={message} onChange={handleChange} />
  );
}

Buyer Journey Intercept

Block checkout progression with validation:

import { useBuyerJourneyIntercept } from "@shopify/ui-extensions-react/checkout";

function AgeVerification() {
  const [verified, setVerified] = useState(false);

  useBuyerJourneyIntercept(({ canBlockProgress }) => {
    if (!verified && canBlockProgress) {
      return {
        behavior: "block",
        reason: "Age verification required",
        errors: [
          {
            message: "Please verify your age to continue",
          },
        ],
      };
    }
    return { behavior: "allow" };
  });

  return (
    <Checkbox checked={verified} onChange={setVerified}>
      I confirm I am 21 or older
    </Checkbox>
  );
}

Post-Purchase Extensions

Create Post-Purchase Extension

shopify app generate extension
# Select: Post-purchase UI

Post-Purchase Upsell

// src/PostPurchase.jsx
import {
  extend,
  render,
  useExtensionInput,
  BlockStack,
  Button,
  Text,
  Image,
  Heading,
  CalloutBanner,
  Layout,
  TextContainer,
} from "@shopify/post-purchase-ui-extensions-react";

extend("Checkout::PostPurchase::ShouldRender", async ({ storage }) => {
  // Decide whether to show post-purchase
  const upsellProduct = await fetchUpsellProduct();
  await storage.update({ upsellProduct });
  return { render: true };
});

render("Checkout::PostPurchase::Render", () => <App />);

function App() {
  const { storage, done, calculateChangeset, applyChangeset } =
    useExtensionInput();
  const { upsellProduct } = storage.initialData;

  const handleAccept = async () => {
    const changeset = await calculateChangeset({
      changes: [
        {
          type: "add_variant",
          variantId: upsellProduct.variantId,
          quantity: 1,
        },
      ],
    });

    await applyChangeset(changeset.token);
    done();
  };

  const handleDecline = () => {
    done();
  };

  return (
    <BlockStack spacing="loose">
      <CalloutBanner title="Special Offer!">
        Add this item to your order at 20% off
      </CalloutBanner>

      <Layout
        media={[
          { viewportSize: "small", sizes: [1, 0, 1], maxInlineSize: 0.9 },
          { viewportSize: "medium", sizes: [532, 0, 1], maxInlineSize: 420 },
          { viewportSize: "large", sizes: [560, 38, 340] },
        ]}
      >
        <Image source={upsellProduct.imageUrl} />
        <View />
        <BlockStack spacing="tight">
          <Heading>{upsellProduct.title}</Heading>
          <TextContainer>
            <Text size="medium">${upsellProduct.price} (20% off)</Text>
          </TextContainer>
          <Button onPress={handleAccept}>Add to Order</Button>
          <Button onPress={handleDecline} plain>
            No thanks
          </Button>
        </BlockStack>
      </Layout>
    </BlockStack>
  );
}

Customer Account Extensions

// Extend customer account pages
import {
  reactExtension,
  Page,
  Card,
  BlockStack,
  Text,
} from "@shopify/ui-extensions-react/customer-account";

export default reactExtension("customer-account.page.render", () => (
  <CustomAccountPage />
));

function CustomAccountPage() {
  return (
    <Page title="Rewards">
      <Card padding>
        <BlockStack spacing="loose">
          <Text size="large">Your Points: 500</Text>
          <Text>Earn points with every purchase!</Text>
        </BlockStack>
      </Card>
    </Page>
  );
}

Localization

// locales/en.default.json
{
  "welcomeMessage": "Welcome to checkout",
  "giftLabel": "Gift options",
  "verifyAge": "I confirm I am 21 or older"
}

// locales/fr.json
{
  "welcomeMessage": "Bienvenue au paiement",
  "giftLabel": "Options cadeau",
  "verifyAge": "Je confirme avoir 21 ans ou plus"
}

import { useTranslate } from "@shopify/ui-extensions-react/checkout";

function Extension() {
  const translate = useTranslate();
  return <Text>{translate("welcomeMessage")}</Text>;
}

Network Requests

import { useApi } from "@shopify/ui-extensions-react/checkout";

function Extension() {
  const { sessionToken } = useApi();

  const fetchData = async () => {
    const token = await sessionToken.get();

    const response = await fetch("https://your-app.com/api/data", {
      headers: {
        Authorization: `Bearer ${token}`,
      },
    });

    return response.json();
  };

  // Use in useEffect or event handler
}

Testing

Local Development

# Start app with preview
shopify app dev

# Extensions will load in checkout preview

Testing in Checkout Editor

1. Go to Shopify admin > Settings > Checkout
2. Click “Customize”
3. Add your extension block
4. Preview changes

Best Practices

1. Keep extensions fast – Minimize API calls
2. Handle errors gracefully – Show user-friendly messages
3. Support localization – Use translation files
4. Test on mobile – Checkout is often mobile
5. Follow design guidelines – Match Shopify’s checkout style
6. Use progressive enhancement – Graceful degradation

Resources

• Checkout UI Extensions
• Checkout UI Components
• Post-Purchase Extensions
• Customer Account Extensions
• Extension Targets Reference

For backend logic, see the shopify-functions skill.