Checkout Extensibility: Customize the Purchase Funnel on Shopify (Update 2025)

Checkout Extensibility: Customize the Purchase Funnel on Shopify (Update 2025)

Leverage new APIs and UI Extensions to create a unique, high-performance purchasing funnel that meets 2025 requirements.

As of August 2024 , Shopify has replaced the legacy checkout.liquid system with Checkout Extensibility , a suite of app-based tools to customize every step of the checkout without risking breaking your store during updates. With the full deprecation of legacy APIs scheduled for April 1, 2025, it is imperative to migrate and adopt UI Extensions , Shopify Functions , and other recent mechanisms to deliver a smooth, fast, and compliant checkout experience.

1. Why Migrate to Checkout Extensibility?

  • Security and sustainability : checkout.liquid will be deactivated in two phases (August 13, 2024 then August 28, 2025).
  • Upgrade-safe : Your customizations are app-based, isolated from the Shopify core, and survive platform updates.
  • Performance : Lighter scripts, better caching, and edge-side execution via Shopify Functions.

2. The Pillars of Checkout Extensibility

2.1 UI Extensions

Allows you to add visual blocks (banners, forms, upsell) at specific points in the checkout (information, delivery, payment).

  • E.g.: add a product suggestion on the payment page.

2.2 Shopify Functions

Serverless functions that run during the process (discount calculation, dynamic shipping costs) to customize business logic.

  • Ex: automatically apply a promo code based on the basket.

2.3 Checkout Branding API

Allows you to style the checkout logo, colors and fonts while respecting the brand's graphic charter, including on Shop Pay.

2.4 App Blocks & Payments Extensibility

  • App Blocks : Integrate third-party apps (e.g., loyalty programs, pop-ups) directly into the purchase funnel.
  • Payments Extensibility : customization of payment methods and acceptance logic (3D Secure, validations).

3. New Frontier: Post-Purchase Page APIs (2025)

Shopify has introduced dedicated post-purchase APIs for:

  • Dynamic upsells on the thank you page.
  • Integration of workflows (referral programs, surveys).

4. Migration Steps

  1. Audit : Identify current customizations in checkout.liquid .
  2. Extension Selection : Select the required UI Extensions and Functions.
  3. Development : Implement locally via Shopify CLI and test with the checkout editor .
  4. Validation : Test each step (Information, Shipping, Payment) before deployment.
  5. Deployment : Publish your apps and remove the deprecated checkout.liquid .

5. Concrete Cases & Results

  • Example A : Adding a “Gift Request” field in UI Extension → +12% gift orders.
  • Example B : Free shipping function over €100 → +15% average basket.
  • Example C : Post-purchase upsell via API → +8% additional turnover.

Conclusion

Shopify's Checkout Extensibility is now the only way to customize your checkout process reliably and efficiently. By migrating before April 2025, you guarantee an optimal customer experience, enhanced SEO performance, and technical agility for unlimited innovation. At Argonauts Agency , we support your transition to these new APIs to transform every step of the checkout process into a conversion opportunity.

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