Extensions

Extensions let your app inject UI or behaviour into a merchant’s store. Each extension type maps to a specific surface — storefront, checkout, post-purchase, admin — and is declared in your app’s app.json. For declarative business logic (cart transforms, discounts, shipping rates, validation), see Functions — those run server-side and return JSON, not UI.

Extension Types

Storefront Blocks

Liquid blocks merchants drop into theme sections (e.g. product page, homepage).

Checkout UI

Sandboxed iframe rendered at a named slot inside the checkout. Talks back to the host via App Bridge.

Post-Purchase

Iframe rendered on the order status (thank-you) page right after checkout. Smaller wired-action set than checkout UI.

Admin Blocks

Iframe embedded on admin resource detail pages (product, order, customer, etc.).

Admin Actions

Button on an admin resource page that opens an iframe modal.

Admin Print Actions

Generate printable templates for orders, invoices, packing slips.

Email Templates

Override the merchant’s transactional emails for named events.

App Scripts

JavaScript files auto-injected on every storefront page — pixels, chat widgets, floating buttons. No theme edits.

Web Pixels

Sandboxed customer-event listeners (page_viewed, cart_updated, checkout_completed).

Customer Account

Iframe blocks on the new customer-account dashboard, order status, profile, and order list pages.

Order Routing

Rules that pick the fulfillment location for an order at checkout.

App Proxy

Serve dynamic content from your app server on the merchant’s own domain — tracking widgets, account pages, AJAX endpoints.

MCP Provider

Other surfaces declared in app.json:

Storefront snippets — reusable Liquid includes ({% render 'foo' %}).
Storefront embeds — overlay/floating scripts injected at <head> or before </body> per the merchant’s app-embed toggle.
Functions (nine types plus the fulfillment_location_rule dispatch wrapper) — declarative WASM modules that fire on cart verification / order placement.

How It Works

Declare extensions in your app’s app.json (manifest).
Install them into a merchant’s store via POST /api/apps/install-extensions — either inline (extensions: {…}) or by referencing the marketplace catalog (fromCatalog: true).
The platform writes the files under extensions/{domainSlug}/{appHandle}/.
The matching storefront / checkout / admin surface picks them up via /api/apps/extensions, /api/apps/checkout-extensions, /api/apps/admin-extensions, etc.

Extension Directory Layout

After install, every app lives at one path on disk:

extensions/{domainSlug}/{appHandle}/
├── app.json                           # Manifest (must exist)
├── blocks/
│   ├── product-reviews.aqua           # Liquid template
│   └── product-reviews.schema.json    # Block schema
├── snippets/
│   └── review-stars.aqua
├── assets/
│   ├── extension.css
│   └── extension.js
├── admin-actions/
│   └── refund-tool.schema.json
├── print-actions/
│   └── packing-slip.schema.json
├── email-templates/
│   └── order_confirmation.json
└── functions/
    └── shipping-rate.wasm

The host reads from this bundle through a server-side cache. After a manifest change, re-run the install call (which refreshes the cache) or wait up to 60 seconds for the manifest cache to expire.

This directory is for extension artifacts only — .aqua templates, schemas, compiled .wasm functions, static CSS/JS assets. Do not write per-store runtime data (config, state, logs, counters) to disk. App runtime data lives in metafields. See the next section.

Where to store app data

Apps do not write to the platform filesystem for runtime state. Every piece of merchant- or customer-scoped data your app needs to read back later — install config, feature toggles, per-product counters, per-customer state, event logs — is persisted as a metafield. There is no app-owned database on the platform, so apps push public summaries (and private blobs) into metafields scoped to a resource (shop, product, customer, order, …).

Two ways to access metafields

Caller	Endpoint	Auth
Third-party OAuth app	`/api/v1/metafields.json`	Bearer access token + `read_metafields` / `write_metafields` scopes
First-party / internal helper	`/metafields/internal/*`	`x-internal-api-key` shared secret (server-side only)

External app developers integrate via the OAuth API. The internal channel exists for first-party catalog apps shipped with the platform — it short-circuits OAuth and resolves the merchant by domainSlug.

Namespace convention

Use one namespace per app, formatted as app_<handle_with_underscores>:

App handle	Metafield namespace
`channels-hub`	`app_channels_hub`
`foundry-reviews`	`app_foundry_reviews`
`restock-alerts`	`app_restock_alerts`

The app_* prefix is the reserved per-app namespace convention on the platform; it keeps your app’s data isolated from custom (merchant-managed) and from other apps’ namespaces. A few apps additionally publish a public summary under a second, shorter namespace so themes can read it via Aqua:

{% comment %} Private (app-internal) — read/write via metafields API {% endcomment %}
{{ product.metafields.app_foundry_reviews.reviews }}

{% comment %} Public (theme-facing) — same data, simpler key for themes {% endcomment %}
{{ product.metafields.foundry_reviews.rating }}
{{ product.metafields.foundry_reviews.count }}

Owner-type scoping

Pick the owner that matches the scope of the data:

Data scope	`ownerType`	`ownerId`
Per-store app config / install settings	`shop`	(resolved from store)
Per-product counter / summary	`product`	product UUID
Per-variant inventory note	`variant`	variant UUID
Per-customer state (subscription, wishlist)	`customer`	customer UUID
Per-order metadata	`order`	order UUID

Compound config is fine — store the whole blob as a single type: "json" metafield under one key like config. The metafield validator decodes JSON on read so consumers get back an object.

Example: write install config

await fetch('https://api.launchmystore.io/api/v1/metafields.json', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${accessToken}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    namespace: 'app_my_reviews',
    key: 'config',
    type: 'json',
    value: { enabled: true, theme: 'minimal', maxPerPage: 10 },
    ownerType: 'shop',
  }),
});

Example: append to a per-product log

For log-shaped data (click logs, recent reviews, subscriber lists), read the existing JSON array, append, and write back. Cap the array length to avoid unbounded growth — there is no platform-side trimming.

const existing = await getMetafield({
  namespace: 'app_foundry_reviews',
  key: 'recent',
  ownerType: 'product',
  ownerId: productId,
}) || [];

existing.push({ rating: 5, text: 'Loved it', t: Date.now() });
if (existing.length > 50) existing.splice(0, existing.length - 50);

await upsertMetafield({
  namespace: 'app_foundry_reviews',
  key: 'recent',
  type: 'json',
  value: existing,
  ownerType: 'product',
  ownerId: productId,
});

Cache invalidation

Every metafield write fires automatic cache invalidation — both the cached copy of the owning resource and any cached page HTML that rendered it. The next storefront render sees the new value. You do not need to manually invalidate anything.

What not to store as metafields

Large blobs (raw images, video, full PDF documents). Use the file reference type instead — upload to R2 / CDN and store the URL.
High-churn counters that update on every page view (view_count). Batch into hourly aggregates or use a backend counter service.
Cross-store data. Metafields are scoped per store; if you need global app state, run your own backend.

Manifest

app.json declares all extensions in one place. Keys under extensions are camelCase:

{
  "handle": "my-reviews-app",
  "name": "Product Reviews",
  "version": "1.0.0",
  "extensions": {
    "storefrontBlocks": [
      {
        "handle": "product-reviews",
        "title": "Product Reviews",
        "target": "product",
        "schema": { "name": "Product Reviews", "settings": [] }
      }
    ],
    "storefrontSnippets": [
      { "handle": "review-stars" }
    ],
    "storefrontEmbeds": [
      {
        "handle": "review-popup",
        "target": "body",
        "scriptSrc": "https://my-app.example.com/embed.js"
      }
    ],
    "checkoutExtensions": [
      {
        "handle": "trust-badges",
        "target": "checkout-payment-after",
        "iframeUrl": "https://my-app.example.com/checkout/trust-badges.html"
      }
    ],
    "postPurchaseExtensions": [
      {
        "handle": "upsell",
        "target": "post-purchase",
        "iframeUrl": "https://my-app.example.com/postpurchase/upsell.html"
      }
    ],
    "adminExtensions": [
      {
        "handle": "reviews-panel",
        "target": "product.details.block",
        "title": "Reviews",
        "url": "https://my-app.example.com/admin/reviews"
      }
    ],
    "appScripts": [
      {
        "id": "reviews-loader",
        "src": "/api/apps/my-reviews-app/loader",
        "loadStrategy": "defer",
        "position": "head"
      }
    ],
    "webPixels": [
      {
        "handle": "review-prompt-pixel",
        "scriptSrc": "https://my-app.example.com/web-pixel.js",
        "events": ["checkout_completed"]
      }
    ],
    "customerAccountExtensions": [
      {
        "handle": "review-list",
        "target": "customer-account.order-status.block.render",
        "iframeUrl": "https://my-app.example.com/account/reviews.html"
      }
    ],
    "functions": [
      {
        "type": "shipping_rate",
        "handle": "expedited",
        "entrypoint": "dist/shipping.wasm"
      }
    ]
  }
}

Admin actions and print actions are stored as per-handle schema files under admin-actions/ and print-actions/ — not as inline arrays in app.json. The install endpoint writes them; see Admin Actions and Admin Print Actions.

Installing Extensions

Two install modes are supported by POST /api/apps/install-extensions:

Mode A — inline upload

For third-party apps that deliver extension files via API:

await fetch('https://store.launchmystore.io/api/apps/install-extensions', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    Authorization: `Bearer ${accessToken}`
  },
  body: JSON.stringify({
    domainSlug: 'merchant-store',
    appHandle: 'my-reviews-app',
    extensions: {
      blocks: [
        { handle: 'product-reviews', template: '<div>...</div>', schema: { /* ... */ } }
      ],
      snippets: [
        { handle: 'review-stars', template: '...' }
      ],
      assets: [
        { filename: 'extension.css', url: 'https://my-app.example.com/dist/extension.css' }
      ],
      adminActions: [
        {
          handle: 'refund-tool',
          target: 'admin.order-details.action.render',
          title: 'Custom refund',
          appUrl: 'https://my-app.example.com/admin/refund'
        }
      ],
      printActions: [
        {
          handle: 'packing-slip',
          target: 'admin.order-details.print.render',
          title: 'Packing slip',
          template: '<html>...</html>'
        }
      ],
      emailTemplates: [
        {
          event: 'order_confirmation',
          subject: 'Thanks for your order!',
          htmlBody: '<h1>...</h1>',
          enabled: true
        }
      ]
    }
  })
});

The handler writes:

blocks/{handle}.aqua + blocks/{handle}.schema.json
snippets/{handle}.aqua
assets/{filename} (fetched from URL)
admin-actions/{handle}.schema.json
print-actions/{handle}.schema.json
email-templates/{event}.json

Mode B — fromCatalog

For apps already published to the marketplace catalog:

await fetch('https://store.launchmystore.io/api/apps/install-extensions', {
  method: 'POST',
  body: JSON.stringify({
    domainSlug: 'merchant-store',
    appHandle: 'flash-discount',
    fromCatalog: true
  })
});

Copies app.json, blocks/, snippets/, functions/ from the catalog into the per-merchant directory.

Email templates are persisted by the platform during install. The file written here is a read-only preview — the authoritative copy is the stored template record.

Uninstalling

await fetch('https://store.launchmystore.io/api/apps/uninstall-extensions', {
  method: 'POST',
  body: JSON.stringify({
    domainSlug: 'merchant-store',
    appHandle: 'my-reviews-app'
  })
});

Removes the entire extensions/{domainSlug}/{appHandle}/ directory. Asset cache + manifest cache are invalidated automatically.

Storefront Block Schemas

Storefront blocks define settings the merchant can configure in the theme editor:

{
  "name": "Product Reviews",
  "target": "product",
  "settings": [
    { "type": "text",     "id": "title",          "label": "Section Title", "default": "Customer Reviews" },
    { "type": "checkbox", "id": "show_rating",    "label": "Show Average Rating", "default": true },
    { "type": "range",    "id": "reviews_per_page", "label": "Reviews Per Page", "min": 5, "max": 50, "step": 5, "default": 10 }
  ]
}

Inside the .aqua template, settings are available as block.settings.* (or block.<id> — both work; the Aqua engine auto-resolves to .settings.<id>).

Targets — Quick Reference

Storefront blocks

index — Homepage
product — Product pages
collection — Collection pages
cart — Cart page
article — Blog articles
page — Custom pages

Checkout UI (currently wired slots)

checkout-contact-after
checkout-shipping-after
checkout-shipping-method-before
checkout-payment-before
checkout-payment-after
checkout-order-summary-before
checkout-order-summary-after
purchase.checkout.cart-line-list.render-after
purchase.checkout.reductions.render-after
purchase.checkout.actions.render-before
purchase.thank-you.block.render
purchase.order-status.block.render
purchase.thank-you.cart-line-list.render-after
purchase.order-status.cart-line-list.render-after

Full list: Checkout UI Extensions.

Admin blocks

product.details.block
order.details.block
customer.details.block
collection.details.block
discount.details.block
26 total — see Admin Blocks.

Admin actions

admin.order-details.action.render (more shipping as resource pages wire up)

Admin print actions

admin.order-details.print.render

Email templates

Replace built-in transactional emails for named events:

order_confirmation (MVP-wired)

Full event list: Email Templates.

Extensions Overview

Extensions

Extension Types

Storefront Blocks

Checkout UI

Post-Purchase

Admin Blocks

Admin Actions

Admin Print Actions

Email Templates

App Scripts

Web Pixels

Customer Account

Order Routing

App Proxy

MCP Provider

How It Works

Extension Directory Layout

Where to store app data

Two ways to access metafields

Namespace convention

Owner-type scoping

Example: write install config

Example: append to a per-product log

Cache invalidation

What not to store as metafields

Manifest

Installing Extensions

Mode A — inline upload

Mode B — fromCatalog

Uninstalling

Storefront Block Schemas

Targets — Quick Reference

Storefront blocks

Checkout UI (currently wired slots)

Admin blocks

Admin actions

Admin print actions

Email templates

See Also

​Extensions

​Extension Types

Storefront Blocks

Checkout UI

Post-Purchase

Admin Blocks

Admin Actions

Admin Print Actions

Email Templates

App Scripts

Web Pixels

Customer Account

Order Routing

App Proxy

MCP Provider

​How It Works

​Extension Directory Layout

​Where to store app data

​Two ways to access metafields

​Namespace convention

​Owner-type scoping

​Example: write install config

​Example: append to a per-product log

​Cache invalidation

​What not to store as metafields

​Manifest

​Installing Extensions

​Mode A — inline upload

​Mode B — fromCatalog

​Uninstalling

​Storefront Block Schemas

​Targets — Quick Reference

​Storefront blocks

​Checkout UI (currently wired slots)

​Admin blocks

​Admin actions

​Admin print actions

​Email templates

​See Also

Extensions

Extension Types

How It Works

Extension Directory Layout

Where to store app data

Two ways to access metafields

Namespace convention

Owner-type scoping

Example: write install config

Example: append to a per-product log

Cache invalidation

What not to store as metafields

Manifest

Installing Extensions

Mode A — inline upload

Mode B — fromCatalog

Uninstalling

Storefront Block Schemas

Targets — Quick Reference

Storefront blocks

Checkout UI (currently wired slots)

Admin blocks

Admin actions

Admin print actions

Email templates

See Also