Checkout Extensibility

We customize the Shopify checkout the supported way — Checkout UI extensions, validation and Functions — so you can add fields, rules and logic without breaking upgrades or compliance.

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The checkout, and the extension targets you are allowed to build intoCOM · 04

Overview

Checkout changes that survive updates

Shopify's checkout extensibility replaces the old checkout.liquid approach with supported extension points: Checkout UI extensions for the interface, Functions for validation and shipping or payment logic, and order attributes for capturing extra data.

Most of this lives on Shopify Plus. We're upfront about that: full checkout customization, branding APIs and delivery or payment Functions require a Plus plan. We scope to what your plan supports and build it so it survives Shopify's updates.

Supported, not hacked: We use Shopify's official extension points, so customizations keep working through checkout updates instead of breaking.
Honest about limits: We tell you upfront which changes are Plus-only and which the checkout simply won't allow, before any work starts.
Conversion-minded: Every field, rule or upsell is weighed against checkout friction, not added just because it's possible.

Discuss your project

Checkout extension points

Where a checkout requirement can actually live, and which ones need Plus.

Cart

Cart transform Function

Information

Checkout UI extension

Shipping

Delivery customization

Shopify Plus

Payment

Payment customization

Shopify Plus

Thank you

Post-purchase extension

Validation runs across cart and checkout — order minimums, restricted regions, mixed-cart rules.

checkout.liquid is not an extension point on new builds.

What's included

What the engagement covers

Checkout UI extensions (custom fields & content)
Cart & checkout validation via Functions
Shipping & payment customization (Plus)
Order attributes & custom line-item data
Customer-specific and B2B checkout flows
Branding & checkout settings configuration

Technologies

Shopify Plus
Checkout UI extensions
Shopify Functions
GraphQL
Order attributes
TypeScript

Use cases

Where this helps most

Custom checkout fields
Capturing gift messages, PO numbers, delivery notes or tax IDs as order attributes at checkout.
Validation rules
Blocking or adjusting orders that fail rules — minimums, restricted regions, mixed-cart conditions — via Functions.
B2B checkout flows
Company-specific fields, terms and logic for wholesale customers within the standard checkout.

Process

How we deliver

Scope & feasibility
We confirm what's possible on your plan, flag Plus-only or unsupported requests, and agree a realistic scope.
Build extensions
We build Checkout UI extensions and Functions in clean, documented code, tested against real checkout paths.
Validate & QA
End-to-end testing across customer types, shipping methods and payment options, plus edge-case validation.
Deploy & support
Controlled deployment with monitoring, plus documentation and post-launch support for your team.

FAQ

Checkout Extensibility

Do I need Shopify Plus for checkout customization?

For most of it, yes. Full checkout UI customization, branding APIs and shipping or payment Functions require Shopify Plus. Some order-attribute and light extension work is more limited on non-Plus plans, and we'll confirm what applies to you.

What happened to checkout.liquid?

Shopify has moved merchants off checkout.liquid to checkout extensibility. We build only on the supported extension points, so your customizations don't break when Shopify updates the checkout.

Can you add upsells or custom logic at checkout?

Yes, within what the platform allows. We can add fields, content and validation via UI extensions and Functions. Anything Shopify doesn't expose an API for, we'll tell you honestly isn't possible.

Proof

Where we have done this

Real projects that used this capability. Every one shipped.

Shopify AppsDevelopment

Checkout Guardian Pro

Shopify app in development that enforces checkout rules, validates purchases and applies operational safeguards.

Shopify
Checkout
Validation
Functions

Shopify StorefrontsProduction

Canvas Lab

EcomLabs contributed theme engineering, checkout work, and CRO to this Shopify storefront, supported by private Node.js applications and API integrations.