Shopify Checkout Extensibility | Built for Plus

When checkout.liquid went away, so did your customisations

Checkout extensibility is the only supported path now. The trouble is doing it without a fragile app stack, a slower checkout, or a rebuild every time Shopify ships.

01

checkout.liquid is gone

The old script and Additional Scripts are deprecated. Anything you relied on there, upsells, fields, trust badges, tracking, needs rebuilding as extensions.

02

App overload at the last step

Five checkout apps fighting for the same real estate slows the page and muddies attribution. You want the outcomes, not the bloat.

03

Rules the theme can't enforce

Hiding express shipping for bulky items, blocking PO boxes, gating payment methods by cart, none of that belongs in Liquid, and merchants keep hacking around it.

04

Validation gaps let bad orders through

No ABN capture, no address checks, no minimum-order guards, so fraud, failed deliveries, and manual clean-up land on your ops team.

05

Tracking broke silently

Pixels that lived in checkout.liquid stopped firing. Web pixel and post-purchase events need re-instrumenting or your reporting lies.

06

Every update is a gamble

Custom checkouts built the wrong way break on Shopify releases. You need work that is upgrade-safe by design, not patched after each incident.

Scope at a glance

What we own, what stays with you, and what sits outside checkout extensibility.

Included	Your side	Out of scope
Checkout UI extensions	Design, build, and deploy	Content and approvals	Full off-platform checkout
Delivery & payment rules	Functions built and tested	Business logic and edge cases	Carrier account setup
Validation	Cart and checkout guards	Rule definitions to enforce	Fraud-tool subscriptions
Tracking	Web pixel and event wiring	Ad and analytics accounts	Attribution modelling
Branding	Branding API styling	Brand assets and tokens	Full theme redesign

Is this the right fit

Built for you if

You are on Shopify Plus, checkout extensibility is a Plus-only capability
You had checkout.liquid customisations and need them rebuilt the supported way
You want checkout upsells, custom fields, or trust content without a heavy app stack
You need delivery or payment rules driven by cart contents, region, or customer
You require ABN, PO-box, or minimum-order validation at checkout
You want the thank-you and order-status pages customised as first-class extensions

Not the right fit if

You are on Shopify (non-Plus), the checkout editor and extensions are not available to you
You want a fully bespoke off-platform checkout, that breaks PCI scope and Shop Pay
You only need a theme or product-page tweak, that is standard theme work, not checkout
You are chasing a specific app's feature that already ships well off the shelf

What we build

Everything is a supported extension or Function, versioned, reviewable, and safe across Shopify releases.

Checkout UI extensions

Upsells, cross-sells, and gift-with-purchase at the checkout step
Custom fields, delivery notes, ABN, gift messages, PO numbers
Trust content, banners, and dynamic messaging by cart or customer
Branding API styling to match your theme, type, and colour
Thank-you and order-status page extensions
Post-purchase upsell offers after payment

Functions & rules

Delivery customisations, hide, rename, or reorder shipping methods
Payment customisations, gate methods by cart, region, or B2B account
Cart and checkout validation, block, warn, or require input
Discount Functions for logic the native rules can't express
Server-side logic in Rust or JavaScript, no theme dependency

Integrations & tracking

Web pixel extensions for GA4, Meta, and server-side tagging
ERP, 3PL, and tax or address-validation service hooks
App block configuration in the checkout editor
Metafield and metaobject wiring for extension data
Rollout via checkout profiles with safe preview and testing

How we work

A tight path from audit to a checkout that stays supported.

01

Audit & discovery

We map your current checkout.liquid, apps, and Additional Scripts, and list what must be rebuilt as extensions. Week 1.

02

Scope & spec

We agree the extensions, Functions, and validation rules, with a checkout profile plan and success measures.

03

Design & branding

We match the checkout to your brand via the Branding API and design each extension surface for clarity and speed.

04

Build

Extensions and Functions built to Shopify's contracts, versioned in Git, reviewed, and kept upgrade-safe.

05

QA & accessibility

Cross-device, cross-region, and payment-scenario testing to WCAG 2.1 AA, on a preview checkout profile.

06

Staged rollout

We publish to a profile, validate live behaviour and tracking, then promote to your primary checkout.

07

Handover & support

Documentation, editor training, and a support window. You own the code and can extend it in-house.

Quality & controls

Checkout is your highest-stakes page. We treat it that way.

WCAG 2.1 AA on every extension surface
Tested across mobile, desktop, Shop Pay, and express wallets
Validated against multiple regions, currencies, and tax scenarios
Web pixel and post-purchase events verified firing before promotion
Staged via checkout profiles, no untested change on live checkout
Built to Shopify extension API contracts for update safety
Version-controlled in Git with peer review on every change

Investment

Typical AUD ranges, scoped after discovery. Price tracks the number of extensions, the complexity of your Functions, and how much checkout.liquid has to be migrated.

Number and complexity of checkout UI extensionsDelivery, payment, and discount Functions requiredValidation rules and their edge casescheckout.liquid and Additional Scripts migration scopeTracking, ERP, and third-party integrationsBranding depth and accessibility requirements

Focused

$6,000–$12,000

A few UI extensions or a targeted checkout.liquid migration.

Standard

$12,000–$25,000

Multiple extensions plus delivery, payment, or validation Functions.

Advanced

$25,000–$45,000+

Full migration, custom Functions, integrations, and staged rollout.

Frequently asked questions

Yes. Checkout UI extensions, the checkout editor, and checkout branding are Plus-only. On non-Plus plans the checkout stays locked, so this service applies to Plus stores.

We audit everything living in checkout.liquid and Additional Scripts, then rebuild each piece as a supported extension, Function, or web pixel. Nothing carries over automatically.

No. Extensions run in Shopify's sandbox, and Functions run server-side, often faster and lighter than the app stack they replace. We test performance before promoting.

Yes. Those are supported extension surfaces now, so we can add tracking, content, referrals, or post-purchase offers there as first-class extensions.

Apps built on checkout extensibility keep working alongside ours. Apps that still rely on the old script will not, we flag those in the audit and rebuild the capability if needed.

You do. Extensions and Functions live in your Git repository under your app, fully documented, so your team or any agency can maintain and extend them.

A focused set of extensions is typically 2–4 weeks. A full checkout.liquid migration with Functions and integrations runs 4–8 weeks, confirmed after discovery.

You get documentation, editor training, and a support window. Because everything is built to Shopify's contracts, it stays stable across releases rather than breaking on updates.

Yes. Delivery and payment customisation Functions handle method visibility and gating, and checkout validation can block, warn, or require input based on the cart.

Related services

Get your checkout customisations back, supported

Book a call and we will audit your current checkout, flag what checkout.liquid left behind, and scope the extensions and Functions to rebuild it safely.

Book a call