Shopify Functions

Shopify Functions are WebAssembly (WASM) units of business logic that extend the Shopify checkout, order, and fulfillment pipelines. They execute in a sandboxed runtime on Shopify's servers and have strict constraints: 5ms execution window, 256KB binary limit, no async I/O, no outbound HTTP to unknown hosts, and 30-point GraphQL query complexity ceiling.

Architecture & Execution Model

Function Lifecycle:

1. Merchant installs your app; metafield definitions are registered
2. App reads merchant configuration from metafields (Shop, Product, Collection scopes)
3. On checkout/order event, Shopify invokes your function with Input JSON payload
4. Function executes WASM bytecode, applies business logic, returns JSON output
5. Output mutations are applied atomically to the checkout/order state