A/B test developer for hire
I build and ship the code behind client-side A/B tests: the variation JavaScript and CSS, the QA, and a clean revert. Most of the work has been on Screwfix's Next.js Pages Router site, where sitewide tests passed first-time engineering review. Split testing and experimentation across Optimizely, VWO, Convert and the rest, written to survive production: SPA-aware, flicker-free, with accessibility built in. Available for direct briefs and as overflow capacity for CRO and experimentation teams.
Available to hire now
Direct briefs or overflow build capacity, with a reply within one UK business day.
What ships, and why it survives production
Plenty of A/B test code works in the editor preview and falls apart in production. SPA route changes never re-trigger the variant. Late-rendering elements miss it entirely. The page flickers as the control flashes before the variation paints, and the engineering team bounces the build before the test even starts. The difference is in how the variation code is written.
- SPA-aware activation that re-applies on route changes and tears the variant down on navigation away, rather than trusting the platform snippet to do it.
- Variation code for a hostile DOM, polling for late-rendering targets instead of guessing a timeout, so the variant lands every time.
- Anti-flicker that hides the element, not the page, so the control never flashes and Core Web Vitals stay inside budget.
- Accessibility built in, the focus order, names and live-region announcements the brief usually leaves out, because client engineering will check them.
- QA that passes first-time review, hand-written test code, a clean revert, and a handover the client team can read.
Platforms I build A/B tests on
The variation code is platform-aware, but the engineering carries across all of them. Each platform has its own page on how the builds work:
A/B tests I've shipped
- Desktop search immersive UI (Screwfix, Optimizely)
- Bestsellers carousel (Avon, Dynamic Yield)
- Trade-price prominence (Travis Perkins, Monetate)
- Customer gallery homepage (Luxury Flooring, Convert.com)
Field notes on A/B testing
The specific failures that come up building client-side tests, each one with the fix and the code:
- A/B tests that die on SPA route changes
- When your A/B test can't find the element
- Stop A/B test flicker without tanking Core Web Vitals
- Accessible A/B test variants: focus, ARIA and screen readers
Hire an A/B test developer
For A/B test and split-test builds, overflow capacity for CRO and experimentation teams, or to discuss a specific test idea. I respond within one UK business day.