Custom Checkout Logic & Functions
Implement reliable, testable checkout logic using Shopify Functions – when native settings are not enough.
The problem
Your checkout rules do not fit into Shopify standard discount or shipping logic. You need to hide payment methods based on order value and customer tags. You want to apply tiered discounts that combine product mix, customer segment, and order history. You have tried native discounts and scripts, but they are either too rigid or too unreliable. You are worried about edge cases: what if a discount stacks incorrectly? What if a customer gets free shipping when they should not? Every promotional period creates anxiety because you are not confident the checkout logic will work correctly.
Why it happens
Checkout customization requires programmatic control, but the options are limited and risky. Shopify Scripts (deprecated) were powerful but difficult to test and debug. Native discounts are composable but not flexible enough for complex business logic. Shopify Functions (the modern solution) give you the control you need, but require careful architecture: they run on every checkout calculation, must be performant, and need comprehensive testing. The root challenge is building Functions that are deterministic, well-tested, and maintainable - not just making it work but engineering it properly.
Your options
We believe in honest recommendations. If native Shopify or an app will work, we'll tell you. Custom builds are for when they won't.
Native Discounts & Shipping Rates
Built-in discount codes, automatic discounts, and shipping profiles. Limited combinability and customization.
When to use
Simple promotional logic: percentage off, buy-X-get-Y, free shipping over $X. Standard shipping rules by weight or price.
Discount & Checkout Apps
Apps that extend native capabilities with additional rules and conditions. May not integrate perfectly with all payment methods.
When to use
Moderately complex logic that an app supports: tiered pricing, volume discounts, customer-specific rules. Willing to pay per-order fees.
Shopify Functions (Custom Built)
Fully custom checkout, discount, and payment logic running as Shopify Functions. Complete control with comprehensive testing.
When to use
Complex business rules that do not fit any app, high order volume where per-order fees are expensive, or need perfect reliability (no discount bugs).
Our recommended architecture
Shopify Functions for checkout, payment, and discount customization with a robust testing framework. Functions are stateless and idempotent. Configuration lives in metafields for easy updates without redeployment.
Define business rules and edge cases comprehensively
Build Shopify Functions with clean separation of logic
Implement configuration layer (metafields or external service)
Create comprehensive test suite: unit tests and integration tests with real checkout sessions
Deploy Functions with staged rollout (percentage of checkouts)
Monitor checkout completion rate and error logs
Iterate based on real checkout data and merchant feedback
Example outcomes
100% reliable discount application - zero customer complaints about incorrect pricing
Support for complex B2B pricing: tiered discounts based on order history and customer segment
Payment method hiding based on risk score reduced fraud chargebacks by 34%
Promotional periods run smoothly without manual verification or emergency fixes
Related Services
Ready to solve this problem?
Book a call and we'll walk through your specific situation, share relevant examples, and give you a clear path forward.