Shopify Plus Certified

Shopify Plus Checkout Extensibility Agency

Custom checkout UI extensions, Shopify Functions, and B2B wholesale portals for high-volume US & UK merchants.

Book a Checkout Extensibility Audit →See our Plus Migration work

✓ Overlapping US (EST) & UK (GMT) sprint hours✓ 100% Code ownership & clean GitHub handover✓ Fixed-scope & fixed-price quotation

Shopify Plus Checkout Extensibility Agency Architecture Blueprint

THE CHECKOUT EXTENSIBILITY PROBLEM

Legacy checkout scripts are a liability, not an asset

Shopify is sunsetting checkout.liquid for Plus merchants. If your checkout is built on script editor or injected JS, you're one platform update away from a broken purchase flow — and a blocked Q4 peak.

⚠ 100% deprecated

Script Editor Deprecation (August 2025)

Shopify removed Script Editor. Merchants still relying on it face broken discount logic during peak season, with no fallback.

⚠ Locked out of new features

Checkout.liquid Sunset

Customised checkout.liquid themes are frozen — no new Shopify features (Shop Pay improvements, B2B, new payment methods) reach them.

⚠ B2B = 32% of Plus revenue

B2B Wholesale Complexity

B2B buyers expect net-30 terms, PO number fields, company-level pricing, and multi-location shipping — none of which standard checkout supports out of the box.

⚠ 900ms avg. script overhead

Checkout Performance Tax

Third-party checkout apps inject render-blocking scripts that add 400–900ms to checkout load — directly reducing purchase completion rates.

OUR CHECKOUT EXTENSIBILITY STACK

Native Checkout UI Extensions with zero legacy debt

We rebuild your checkout using Shopify's official Checkout UI Extension framework and Shopify Functions API — delivering branded, performant checkout flows that are maintenance-free through every platform upgrade.

✓Checkout UI Extensions for custom branding, upsells, gift messages, and trust badges

✓Shopify Functions for server-side discount tiers, tiered shipping logic, and custom payment filtering

✓B2B portal configuration: company profiles, net-term payment methods, PO number fields

✓Multi-currency and multi-market checkout with Shopify Markets

✓Flow automations for post-purchase actions: loyalty points, fulfilment routing, CRM updates

VERIFIED TECH STACK

Checkout UI Extensions

Platform

Official Shopify Plus checkout customisation framework

Shopify Functions

Platform

Server-side business logic: discounts, shipping, payment

Shopify B2B APIs

Commerce

Company profiles, net terms, price lists, location-based shipping

Shopify Markets

Internationalisation

Multi-currency, multi-language checkout routing

Shopify Flow

Automation

Post-purchase workflow automations and CRM triggers

Admin GraphQL API

Backend

Programmatic catalogue, pricing, and order management

PROVEN RESULTS · Checkout Extensibility Migration

Migrated from checkout.liquid to Checkout UI Extensions — checkout conversion up 21%

A Shopify Plus health brand faced Script Editor deprecation two months before BFCM. We migrated their custom discount tiers and gift-with-purchase logic to Shopify Functions, rebuilt the checkout UI in Checkout UI Extensions, and delivered zero-downtime cutover — with a 21% lift in purchase completion.

+21%

Checkout conversion rate

-64%

Checkout JS payload

2 weeks

Migration & QA timeline

Post-launch defects

“The new checkout is faster, cleaner, and our BFCM was our best ever. Devan Labs delivered on a timeline no other agency would commit to.”

— Head of eCommerce, US Health & Wellness Brand

WHAT YOU GET

Engineering deliverables checklist

Every engagement includes fixed scope, clear milestone verification, and direct engineer access with zero junior account managers in between.

✓

Checkout UI Extension build

Custom branding, trust signals, upsell widgets, gift messages

Week 1–2

✓

Shopify Functions migration

Custom discount tiers, tiered shipping rules, payment method filters

Week 1–3

✓

B2B portal setup

Company profiles, net-30 terms, PO fields, price lists

Week 2–4

✓

Multi-market checkout

Currency, language, and tax routing via Shopify Markets

Week 3–4

✓

Flow automation suite

Post-purchase loyalty, fulfilment routing, CRM sync triggers

Week 4

✓

QA & regression suite

Cross-browser, cross-device checkout testing with edge-case discount scenarios

Week 4–5

TECHNICAL FAQS

Frequently asked questions

Specific answers to common technical, timeline, and architectural questions from US and UK ecommerce directors.

What is Checkout Extensibility and why does it matter for Shopify Plus?+

Checkout Extensibility is Shopify's official framework for customising the checkout using native UI Extensions and Functions — replacing the old checkout.liquid and Script Editor. It's future-proof, upgrade-safe, and unlocks access to all new Shopify checkout features including Shop Pay improvements and B2B tools.

How long does a checkout.liquid to Checkout Extensibility migration take?+

For most Plus stores we deliver the full migration — including custom discount logic and branding — within 4–6 weeks. Stores with complex B2B or multi-market requirements may take 8 weeks. We always include a parallel-run period so you can test the new checkout before cutover.

Can you replicate our existing Script Editor discount logic in Shopify Functions?+

Yes. Shopify Functions run server-side in a sandboxed Wasm environment and support all the discount, shipping, and payment customisation patterns that Script Editor did — plus more complex logic like stacking rules and tiered B2B pricing that Script Editor could never handle.

Do you handle B2B-specific checkout requirements like PO numbers and net terms?+

Absolutely. We configure Shopify B2B APIs to add company profiles, net-term payment methods, PO number line item fields, location-based shipping, and price lists — all native to Shopify Plus with no third-party app dependency.

Will you support us through BFCM or a major campaign launch?+

Yes. Our retainer clients get a named engineer available during peak campaigns. We also offer a standalone BFCM readiness audit covering checkout load performance, discount logic smoke-testing, and inventory webhook resilience.

RECOMMENDED DEEP DIVE ARCHITECTURE GUIDE

Read our in-depth technical playbook

Learn how our engineers tackle real-world Shopify performance, data migration, and architecture constraints.

Read Technical Guide →

RAPID 3-DAY TURNAROUND · NO OBLIGATION

Let's audit your store architecture

Book an architecture call or send your store URL for a free 40-point technical code, speed, and conversion audit. Delivered in 3 business days.

Book a Checkout Extensibility Audit See our Plus Migration work