Checkout migration is a business-rule exercise first. The goal is supported behavior, not a line-for-line recreation of legacy scripts.
Inventory current behavior
List every checkout UI change, validation, discount, delivery, payment, tracking and post-purchase rule. Identify who depends on it and what happens when it fails.
- Document triggering conditions
- Capture customer and market differences
- Separate requirements from workarounds
- Record analytics and consent behavior
Map supported Shopify surfaces
Select the smallest supported surface for each requirement after confirming plan, market, B2B and payment limitations.
- Checkout UI extensions for appropriate interface needs
- Shopify Functions for supported business logic
- Pixels and customer events for measurement
- Apps or services with explicit ownership
Design configuration and failure states
Rules need merchant controls and understandable fallback behavior. Treat empty data, ineligible carts and unavailable services as expected states.
- Define configuration ownership
- Validate missing and malformed inputs
- Keep customer messages specific
- Log operationally important failures
Test beyond the default cart
Acceptance criteria should cover markets, customer states, accelerated checkout, subscriptions and the combinations most likely to expose rule conflicts.
- Eligible and ineligible carts
- Mobile, keyboard and assistive technology
- Delivery and payment combinations
- Rollback and monitoring after release
Use this framework against the actual store.
Review the decision with the catalog, customer journey, systems, team and operating constraints in view. That is where a general framework becomes a responsible implementation plan.