Senior Frontend Developer with JS in London

We are a digital optimisation agency, knitting together digital analytics, SEO and CRO (we call it experimentation) to help deliver better website experiences and increasing conversions for clients. Our founders have over 35 years combined experience in the field and are passionate about helping businesses win with data. We are determined to build the best place to work in digital optimisation.

We’re seeking a skilled Senior Front-End Developer (CRO) with at least 2 years of relevant experience to join our Experimentation team and help us deliver best-in-class website testing services for our clients. As a Senior Front-End Developer (CRO), your primary responsibility will be to take ownership of bringing “variation experiences” to life for our clients. Working closely with analysts, strategists, and designers, you’ll build high-quality test variations that help solve user experience challenges and validate new ideas.

You’ll be expected to work confidently with testing platforms such as AB Tasty, Optimizely, VWO, or Webtrends Optimize, and to share your expertise to support colleagues and clients. We work with clients of all sizes, so you’ll have the opportunity to lead on a variety of projects, exercise independence in your work, and contribute ideas that influence experimentation strategy.

You’ll also play a key role in upholding best practices in development, mentoring junior team members where appropriate, and continuously evolving our approach to CRO implementation. As a Senior Front-End Developer, we’ll rely on your proven expertise in experimentation and front-end development to deliver high-quality solutions, guide best practices, and drive innovation across client projects.

• Leading the onboarding of testing tools to client websites, including technical setup, configuration, and troubleshooting across domains.
• Owning the technical solution design for experiments, considering client requirements, testing platform capabilities, and long-term maintainability.
• Building high-quality HTML, CSS, and JavaScript code to transform designs into polished, interactive variation experiences.
• Managing the end-to-end configuration of tests within client-selected A/B testing platforms, including targeting, audience segmentation, goals, and analytics integrations.
• Acting as a trusted technical partner for clients and their development teams, building strong relationships and ensuring smooth communication on code changes and experiment delivery.

Agency-side experience, or client-side experience working on complex, multi-site brands. Strong background in front-end development with proficiency in HTML, CSS, and Javascript. Demonstrated experience designing and implementing experiments using A/B testing or personalisation platforms. Strong problem-solving skills, attention to detail, and ability to manage multiple projects simultaneously. Understanding of SEO principles, performance optimisation, and accessibility standards.

Pension scheme (4% from you and 4% from us, 8% in total). ~25 days holiday per year with the opportunity to roll days into the next year. ~ A hybrid working approach; 2 days in our Shoreditch office, and we will help get you set up with a home office set-up that suits you. ~ We have plenty of opportunities for development and growth. You’ll directly shape the benefits we offer as we start to scale – whether that’s birthday days off, how we contribute to a better society or the type of ice cream we buy. People LOVE ice cream.