I write the experiment code that runs on your live revenue pages, the ones too important to break. Every test ships clean and reverts without a trace, so the only thing your visitors notice is the result.
01 // selected work
experiments · builds · writeups
shipped to production
Selected experiments showing the kinds of problems I solve: SPA-aware UI, server-load mitigation, enterprise platform quirks, and accessibility-compliant variants.
Large UK home improvement retailer
Vertical search overlay had low engagement. F-pattern reading suggested a landscape layout could lift SRP progression.
Built a darkened focus-state overlay, repositioned the search element to a landscape layout, and added search-term-driven subcategory chips for Variant 2. Maintained existing product-suggestion logic to isolate layout as the variable. Two variants shipped sitewide on desktop.
Read the case study →Why your GA4 split never matches the platform
GA4 shows 60:40 when the testing platform shows 50:50. Random, unstable, never matches, and the experiment code is rarely the actual cause.
Walks through the four root causes of GA4/platform Sample
Ratio Mismatch on SPAs (data layer timing, beacon loss, virtual pageview
context, bot traffic) and the Tealium/GTM tracking pattern (with
utag.link intercept and payload mirroring) that fixes most of
them.
UK vehicle scrappage and valuation service
A revenue-critical Vehicle Details step, redesigned to a cleaner single column with the offer in a banner, delivered client-side through Convert on a React single-page app with no access to the codebase.
Re-skinned React's own form rather than rebuilding it: CSS for everything it can do so it survives re-renders, JavaScript only for the banner, icon and CTA, kept idempotent and re-applied across the funnel's route changes, with the vehicle read live from localStorage. Built and in QA.
Read the case study →abtestrig, a CRO-specific build tool, open source on GitHub
Every CRO dev rebuilds the same Gulp/webpack rig. Hardcoded loader-script IDs, 8 to 15s rebuilds, page reloads on every CSS tweak, and no way to test interactions between two live experiments before shipping.
Built abtestrig around esbuild: sub-200ms builds, a loader
that auto-discovers the active experiment and port (no script edits between
experiments), CSS hot-swap via a stable <style> slot so
the activated state is preserved, stack-mode that runs multiple experiments
in deterministic order for conflict testing, and a shared @lib
helper library so pollerLite/waitForElement stop
getting copy-pasted between projects.
UK ground engineering / residential subsidence
Geobear runs a HubSpot CMS estate of 50+ pages across several brand variants, all powered by the same theme. The brief: a new residential landing page with a different layout and modules, without putting the 50+ live pages at risk.
Cloned the live theme into a parallel build via
hs cms fetch / hs cms upload, then shipped nine custom
modules from scratch: sticky nav, hero with background video, case carousel,
get-advice flow, logos, testimonials, video gallery, CTA banner, and a Leadoo
form wrapper. Deferred Swiper init via IntersectionObserver, a
ResizeObserver shim for sticky-nav padding under HubSpot's
overflow: hidden wrappers, CSS custom properties for the design
system, and inline schema.org JSON-LD (HowTo,
ItemList, Review) that passed the Rich Results
Test.
Large UK home improvement retailer
Google Shopping landers were exiting PDPs and re-entering through Shopping multiple times when the specific product didn't fit. Top-50 power-tool SKUs by click volume were the priority.
Built a sticky "follow-me" similar-products carousel
scoped to the product's category. Scrapes the breadcrumb-derived PLP at a
price-bound API call, caches results in sessionStorage so
subsequent PDPs in the same category render instantly. V2 layers a brand
filter for brand-loyal users.
02 // how i work
hand-written test code
QA'd · accessible · reverts clean
Comfortable with Tealium, GA4, Adobe Analytics and most consent-management providers. Familiar with Magento, Shopify Plus, Next.js, and AEM host stacks. Also build custom HubSpot CMS modules (HubL) where the brief calls for it.
03 // clients & partners
retailers · insurers · DTC
direct + via agencies
Experiments and builds shipped for retailers, insurers, charities, and DTC brands, both directly and through agencies and CRO partners.
// experiments shipped for
// agency & direct partners
04 // field notes
deep dives on the bugs
that come up on real builds
Writeups from real client work on the specific failures that come up building experiments on modern stacks, and how I fix them.
Why your Optimizely experiment won't fire on SPA route changes
Why your A/B test variation won't stick on a React input
Why your A/B test can't find the element (it rendered late)
Stop your A/B test from tanking Core Web Vitals
Accessible A/B test variants: focus, ARIA, and screen readers
Why your A/B test flickers, and how to stop it
Optimizely vs VWO vs Convert for developers
abtestly vs Convert: an honest comparison
05 // get in touch
open to new projects
UK + US business hours
For project enquiries, overflow capacity, or to hire an A/B test developer for a conversion rate optimisation build. I respond within one UK business day.