Write the rule in plain business language, enumerate inputs and exceptions, and confirm that a supported Function API owns that decision.
Keep configuration merchant-friendly, minimize input queries and test mixed carts, currencies, customer states and missing data.
Content and platform references reviewed on .
Choose the API that owns the decision
Functions extend defined Shopify business-logic surfaces. Start by naming the decision: a discount, delivery presentation, payment rule, validation or another supported operation. A requirement that needs an unrelated back-office workflow should not be squeezed into a Function simply because it must run automatically.
Model inputs and configuration explicitly
List the cart, product, customer or configuration data the rule needs, then confirm it is available in the chosen input schema. Keep the query focused and validate missing values. Avoid hardcoding business choices that the merchant will regularly change, but do not expose configuration without clear validation and defaults.
Test conflicts and boundaries
Test mixed carts, quantities at the eligibility boundary, currency differences and combinations with other active rules. Check whether the chosen API can represent the intended result. The storefront message and the server-side outcome must agree, especially where customers are asked to change the basket to continue.
Include plan eligibility and operational ownership
Confirm the availability of the selected Function API and the app distribution model for the merchant’s plan. Document how the rule is enabled, updated and disabled, and who investigates unexpected results. A deterministic rule still needs monitoring, maintained configuration and regression checks when catalog or promotion logic changes.
Checks for this implementation
- Validate the input query and output against the target Function schema.
- Test empty configuration, exclusions and overlapping promotions.
- Provide merchant instructions for activation and safe rule changes.
Common mistake to avoid
Forcing unrelated workflows into a Function creates opaque logic and maintenance problems for future teams.
A well-scoped Function makes important logic fast, predictable and easier to govern than storefront workarounds.
Platform references
Continue with Shopify Functions development, or discuss the requirements for your store.
