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Shopify Functions Decision Table

By Graham O'Shea, Founder and Lead Developer  ·  1 August 2026  ·  Part of The Shopify Development Guide

Shopify Functions run under published limits, and those limits decide the design before anyone writes code. This table matches a rule to one of the nine APIs, then checks it against the numbers.

What Is In The Shopify Functions Decision Table

  • Three questions that decide whether a rule belongs in a Function at all.
  • A table matching what a rule decides to which of the nine Function APIs.
  • The documented limits, including which are conditional on cart size.
  • How to size a rule against your own largest cart rather than your average one.
  • Three routes when it does not fit, in the order worth trying them.
  • Six things to confirm before signing off a build.

Why The Limits Come Before The Design

A Function has a fixed execution budget, and a rule that grows with the square of the line count can pass testing and fail on a trade order. Shopify's own guidance names that risk, recommending Rust specifically to avoid a function failing with large carts. Checking the numbers first is cheaper than discovering them later.

The full reasoning is in the article this accompanies: What Actually Belongs In A Shopify Function.

Prefer A Second Opinion On Where Your Rule Belongs?

The Shopify store audit is free. The form asks for your store URL and a note on what is eating the time, and a rule you cannot place is a reasonable thing to put in that box.

Request The Free Shopify Store Audit