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Shopify Functions Decision Table

By Graham O'Shea, Founder and Lead Developer1 August 2026Part 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