Checkout is where growth-minded brands win or lose. Across ecommerce, the average cart abandonment rate hovers around 70 percent, and a significant share of drop-offs stem from fixable UX issues and trust gaps. According to the Baymard Institute’s analysis of 50 studies, 19 percent of shoppers cited not trusting a site with their card and 18 percent cited a long or complicated checkout among top reasons for abandonment, with the overall abandonment rate at 70.22 percent in 2025. The same report notes many issues can be solved through design improvements. As a Shopify-first agency, BoomSprint builds conversion-focused checkouts that are upgrade safe and measurable, using Shopify’s Checkout Extensibility.
What Checkout Extensibility really unlocks
Checkout Extensibility is Shopify’s app-based framework for customizing checkout without editing core templates. Merchants can add UI blocks, business logic with Functions, and measurement via pixels using the checkout editor, all while staying upgrade safe. Shopify’s own overview explains that apps can place blocks at defined targets, and that the checkout editor lets merchants position extension blocks where they belong. The “Apps in checkout” guide also clarifies that checkout.liquid is deprecated for in-checkout pages and will sunset on Thank you and Order status pages in August 2025, so the future is extensions.
The upgrade to a one-page layout is a major win for speed and clarity. Shopify’s one-page checkout, rolled out broadly in September 2023, condenses steps into a single, optimized screen and integrates accelerated wallets like Shop Pay. The one-page checkout article describes how brands can toggle layouts in the editor and keep customizations upgrade safe through Checkout Extensibility. That streamlined experience sets the stage for the three highest impact levers: relevant upsells, explicit trust signals, and robust analytics.
High intent upsells that respect the flow
Done right, upsells increase average order value without derailing the purchase. Shopify supports pre-purchase, post-purchase, and Thank you page experiences through extensions. The tutorials linked from Shopify’s “Apps in checkout” page show how to build pre-purchase product offers, post-purchase offers, and post-purchase surveys on the Thank you and Order status pages.
If you want to unlock the cleanest lift, start with post-purchase upsells. The official guide to post-purchase offers explains that offers render after payment and before the Thank you page, and that developers can compute taxes and shipping with calculateChangeset and then applyChangeset to edit the order. The same guide notes that post-purchase extensions are in beta and require access approval for live stores, but can be tested freely in development stores. Because payment is already captured, post-purchase offers avoid jeopardizing the initial conversion while giving buyers a fast add-on path that feels native.
Pre-purchase upsells are powerful for subscription add-ons, warranties, or low-friction bundles when the offer directly helps the buyer complete the job. Lean on Shopify Functions for custom discount logic and use Checkout UI extension blocks to keep messaging contextual. Shopify’s UX for checkout guidelines emphasize transparency, optionality cues, and reducing friction, which should govern any upsell copy or components you introduce.
Practical checklist for upsells:
One clear offer with a concise value proposition and transparent pricing.
Visual alignment with your brand through checkout branding and the editor.
Social proof only where it aids decision making, not as decoration.
Trust is a conversion feature
Trust shapes willingness to pay and speed to completion. In Baymard’s latest breakdown of reasons for abandonment, 19 percent of shoppers did not trust the site with card details and 10 percent said there were not enough payment methods. At the same time, Shopify’s own analysis reports that Shop Pay can lift conversion by as much as 50 percent compared to guest checkout, and even its presence alone can raise lower funnel conversion by 5 percent. Pair that with wallet choice. Nielsen research commissioned by PayPal indicates that large enterprises see a 33 percent increase in checkout conversion when PayPal is selected, and 74 percent of PayPal users are more likely to complete a purchase from an unknown business when PayPal is available.
Translate those signals directly into the interface. Shopify’s UX guidelines for checkout recommend maintaining trust by clearly explaining required fields and costs. Use branding controls and UI extension blocks to:
Display accepted payment methods prominently, including Shop Pay, PayPal, Apple Pay, and major cards.
Surface plain-language security copy and policy links. Shopify’s checkout customization docs show how to use branding and footer content to display store policies and reassurance where shoppers expect it.
Remove nonessential fields and mark optional inputs. This aligns with the guidelines around reducing friction and helps counter the 18 percent who abandon due to long forms.
When trust is visible and friction is minimal, you create a checkout that feels both familiar and fast. Shopify’s study on the best-converting checkout underscores this advantage, noting overall conversion outpaces competitors by up to 36 percent.
Analytics that actually measure checkout improvements
If you cannot measure it, you cannot improve it. Shopify’s Web Pixels API provides a controlled sandbox and a Standard API to subscribe to events like checkout_started, payment_info_submitted, and checkout_completed. The standard events documentation clarifies that checkout_completed fires once per checkout and triggers on the first upsell offer page in a post-purchase flow rather than on the Thank you page. That nuance matters for attribution and funnel drop-off analysis.
Implementation is straightforward. The Shopify Help Center’s pixels guide explains how app pixels and custom pixels are managed in the Customer events section of admin. For advanced teams, the Web Pixels API documentation details access to analytics, browser storage, and init data in a strict sandbox so you can enrich event payloads while respecting privacy. Use a consistent schema for experiments, tag cohorts at checkout_started, and evaluate treatment effects on conversion, AOV, and repayment rates for wallets.
How BoomSprint implements this for brands
Our accelerated model, honed across ecommerce builds, gets you from idea to uplift fast:
Discovery and KPI targeting. We audit existing checkout data, identify Baymard-grade friction points, and set hypotheses tied to conversion and AOV.
Prototype in the checkout editor. We map extension targets and design upsell and trust components in interactive prototypes so stakeholders can feel the flow before any build. Explore our approach in the BoomSprint services overview.
High-end design and build. We apply brand-aligned visuals, motion, and Checkout UI extensions plus Functions and pixels. Everything is modular for future iteration.
QA on mobile, guest, and Shop Pay. Shopify’s own UX guidelines highlight testing across scenarios, so we verify behavior on accelerated wallets, international addresses, and discount states.
Measurement and iteration. We wire the Web Pixels API to capture standard events and run controlled tests. Wins ship, misses are refined.
You can see how we bring polish and performance together in our selected work. For scope and options, the BoomSprint pricing page outlines transparent packages. If you are starting a new store or planning a replatform, get going with Shopify and take advantage of the world’s highest converting checkout using our affiliate link. When you are ready to execute with a partner, contact the BoomSprint team and we will map a fast, design-forward plan.
Resources to go deeper:
Shopify’s one-page checkout guide shows how the new layout streamlines speed and integrates Shop Pay.
The Apps in checkout documentation lists official tutorials for pre-purchase, post-purchase, and Thank you page extensions.
Web Pixels API documentation and Standard events reference provide the event semantics for reliable analytics.
Baymard Institute’s abandonment statistics quantify the opportunity you can unlock by reducing friction and increasing trust.
With thoughtful upsells, visible trust, and verified analytics, Checkout Extensibility becomes a practical lever for compounding conversion gains.
