IF user wants to customize checkout OR add admin UI OR create POS actions OR implement discount rules: → Build an Extension (see references/extensions.md)

IF user wants to customize storefront design OR modify product/collection pages: → Build a Theme (see references/themes.md)

IF user needs both backend logic AND storefront UI: → Build App + Theme Extension combination

Shopify CLI Commands

Install CLI:

npm install -g @shopify/cli@latest

Create and run app:

shopify app init          # Create new app
shopify app dev           # Start dev server with tunnel
shopify app deploy        # Build and upload to Shopify

Generate extension:

shopify app generate extension --type checkout_ui_extension
shopify app generate extension --type admin_action
shopify app generate extension --type admin_block
shopify app generate extension --type pos_ui_extension
shopify app generate extension --type function

Theme development:

shopify theme init        # Create new theme
shopify theme dev         # Start local preview at localhost:9292
shopify theme pull --live # Pull live theme
shopify theme push --development  # Push to dev theme

Access Scopes

Configure in shopify.app.toml:

[access_scopes]
scopes = "read_products,write_products,read_orders,write_orders,read_customers"

Common scopes:

read_products, write_products - Product catalog access
read_orders, write_orders - Order management
read_customers, write_customers - Customer data
read_inventory, write_inventory - Stock levels
read_fulfillments, write_fulfillments - Order fulfillment

GraphQL Patterns (Validated against API 2026-01)

Query Products

query GetProducts($first: Int!, $query: String) {
  products(first: $first, query: $query) {
    edges {
      node {
        id
        title
        handle
        status
        variants(first: 5) {
          edges {
            node {
              id
              price
              inventoryQuantity
            }
          }
        }
      }
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

Query Orders

query GetOrders($first: Int!) {
  orders(first: $first) {
    edges {
      node {
        id
        name
        createdAt
        displayFinancialStatus
        totalPriceSet {
          shopMoney {
            amount
            currencyCode
          }
        }
      }
    }
  }
}

Set Metafields

mutation SetMetafields($metafields: [MetafieldsSetInput!]!) {
  metafieldsSet(metafields: $metafields) {
    metafields {
      id
      namespace
      key
      value
    }
    userErrors {
      field
      message
    }
  }
}

Variables example:

{
  "metafields": [
    {
      "ownerId": "gid://shopify/Product/123",
      "namespace": "custom",
      "key": "care_instructions",
      "value": "Handle with care",
      "type": "single_line_text_field"
    }
  ]
}

Checkout Extension Example

import {
  reactExtension,
  BlockStack,
  TextField,
  Checkbox,
  useApplyAttributeChange,
} from "@shopify/ui-extensions-react/checkout";

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

function GiftMessage() {
  const [isGift, setIsGift] = useState(false);
  const [message, setMessage] = useState("");
  const applyAttributeChange = useApplyAttributeChange();

  useEffect(() => {
    if (isGift && message) {
      applyAttributeChange({
        type: "updateAttribute",
        key: "gift_message",
        value: message,
      });
    }
  }, [isGift, message]);

  return (
    <BlockStack spacing="loose">
      <Checkbox checked={isGift} onChange={setIsGift}>
        This is a gift
      </Checkbox>
      {isGift && (
        <TextField
          label="Gift Message"
          value={message}
          onChange={setMessage}
          multiline={3}
        />
      )}
    </BlockStack>
  );
}

Liquid Template Example

{% comment %} Product Card Snippet {% endcomment %}
<div class="product-card">
  <a href="{{ product.url }}">
    {% if product.featured_image %}
      <img
        src="{{ product.featured_image | img_url: 'medium' }}"
        alt="{{ product.title | escape }}"
        loading="lazy"
      >
    {% endif %}
    <h3>{{ product.title }}</h3>
    <p class="price">{{ product.price | money }}</p>
    {% if product.compare_at_price > product.price %}
      <p class="sale-badge">Sale</p>
    {% endif %}
  </a>
</div>

Webhook Configuration

In shopify.app.toml:

[webhooks]
api_version = "2026-01"

[[webhooks.subscriptions]]
topics = ["orders/create", "orders/updated"]
uri = "/webhooks/orders"

[[webhooks.subscriptions]]
topics = ["products/update"]
uri = "/webhooks/products"

# GDPR mandatory webhooks (required for app approval)
[webhooks.privacy_compliance]
customer_data_request_url = "/webhooks/gdpr/data-request"
customer_deletion_url = "/webhooks/gdpr/customer-deletion"
shop_deletion_url = "/webhooks/gdpr/shop-deletion"

Best Practices

API Usage

Use GraphQL over REST for new development
Request only fields you need (reduces query cost)
Implement cursor-based pagination with pageInfo.endCursor
Use bulk operations for processing more than 250 items
Handle rate limits with exponential backoff

Security

Store API credentials in environment variables
Always verify webhook HMAC signatures before processing
Validate OAuth state parameter to prevent CSRF
Request minimal access scopes
Use session tokens for embedded apps

Performance

Cache API responses when data doesn't change frequently
Use lazy loading in extensions
Optimize images in themes using img_url filter
Monitor GraphQL query costs via response headers

Troubleshooting

IF you see rate limit errors: → Implement exponential backoff retry logic → Switch to bulk operations for large datasets → Monitor X-Shopify-Shop-Api-Call-Limit header

IF authentication fails: → Verify the access token is still valid → Check that all required scopes were granted → Ensure OAuth flow completed successfully

IF extension is not appearing: → Verify the extension target is correct → Check that extension is published via shopify app deploy → Confirm the app is installed on the test store

IF webhook is not receiving events: → Verify the webhook URL is publicly accessible → Check HMAC signature validation logic → Review webhook logs in Partner Dashboard

IF GraphQL query fails: → Validate query against schema (use GraphiQL explorer) → Check for deprecated fields in error message → Verify you have required access scopes

Reference Files

For detailed implementation guides, read these files:

references/app-development.md - OAuth authentication flow, GraphQL mutations for products/orders/billing, webhook handlers, billing API integration
references/extensions.md - Checkout UI components, Admin UI extensions, POS extensions, Shopify Functions for discounts/payment/delivery
references/themes.md - Liquid syntax reference, theme directory structure, sections and snippets, common patterns

Scripts

scripts/shopify_init.py - Interactive project scaffolding. Run: python scripts/shopify_init.py
scripts/shopify_graphql.py - GraphQL utilities with query templates, pagination, rate limiting. Import: from shopify_graphql import ShopifyGraphQL

Official Documentation Links

Shopify Developer Docs: https://shopify.dev/docs
GraphQL Admin API Reference: https://shopify.dev/docs/api/admin-graphql
Shopify CLI Reference: https://shopify.dev/docs/api/shopify-cli
Polaris Design System: https://polaris.shopify.com

API Version: 2026-01 (quarterly releases, 12-month deprecation window)

shopify-development

Shopify Development Skill

ROUTING: What to Build