Lead CRO Developer

Role overview

We are looking for a highly experienced, hands‑on Lead CRO Developer to build and deliver A/B and multivariate experiments across our client accounts. This is fundamentally a development role. The majority of the role is hands‑on coding, implementation, QA and troubleshooting of experiments, not CRO strategy, programme management, or roadmap ownership.

You will take test designs and specifications and turn them into robust, production-ready experiments across enterprise experimentation platforms. As the lead developer, you will also act as the technical escalation point for complex builds and help maintain high development and QA standards, while remaining deeply hands‑on day to day.

• Build A/B and multivariate experiments from supplied concepts, designs and test specifications.
• Write clean, robust JavaScript (ES6+), HTML5 and CSS3 to create experiment variations and functionality.
• Develop experiments within Optimizely and other enterprise testing platforms including VWO, AB Tasty, Convert, Monetate and similar tools.
• Build experiments within modern React and Next.js environments, including single-page applications and dynamically rendered experiences.
• Handle technically complex tests involving DOM manipulation, application state, targeting, customer journeys and dynamic content.
• Where appropriate, develop or support full-stack / server-side and feature experiments using SDKs, APIs and feature flags.
• Implement and validate experiment tracking, events and data-layer requirements using tools such as GTM and Tealium.
• Debug failed or inconsistent experiments, resolve conflicts with client codebases and troubleshoot platform or implementation issues.
• Identify performance issues such as flicker, race conditions or unnecessary page impact and implement appropriate solutions.
• Work directly with client developers where access to the underlying application, APIs, SDKs or data layer is required.
• Review particularly complex experiment builds and provide technical support to other CRO developers when needed.

JavaScript: Advanced JavaScript (ES6+) skills. You must be comfortable writing substantial custom code for experiments rather than relying on visual editors.

HTML & CSS: Strong HTML5 and CSS3 development skills, including responsive implementation and accurate translation of supplied designs.

Optimizely: Strong hands‑on experience building experiments in Optimizely Web. Experience with Optimizely Full Stack / Feature Experimentation is highly valuable.

Experimentation development: Extensive experience personally building and shipping A/B and multivariate tests in live ecommerce or enterprise environments.

React / Next.js: Strong experience developing and debugging experiments on React and Next.js applications, including SPAs.

QA & debugging: Excellent browser developer-tools skills, troubleshooting ability and rigorous cross-browser/device experiment QA.

Tracking & tag management: Experience with GTM and/or Tealium, event tracking and data layers as they relate to experimentation.

Cross-platform delivery: Ability to work confidently across different CMSs, ecommerce platforms, and proprietary client technology stacks.

We are particularly interested in developers with hands‑on build experience across several of the following. Depth of practical development experience is more important than simply having used the platform.

• Optimizely Web
• Optimizely Full Stack / Feature Experimentation
• VWO
• AB Tasty
• Convert
• Monetate
• Webtrends Optimize or equivalent enterprise experimentation platforms

• Type Script.
• Node.js.
• Server-side / full-stack experimentation.
• Experimentation SDK and API implementation.
• Feature flags and server-side…