Senior CRO Front-End Developer

About Hookflash

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 use analytics to understand where barriers to conversion exist and to identify areas of opportunity. We use SEO to continue with diagnostics on where the site could be improved and start rolling out optimisations. And by tying the previous two disciplines with experimentation, we take make sure changes are tested and hypothesis are validated.

We are determined to build the best place to work in digital optimisation. A place where time is not just set aside but actively encouraged, to focus on innovation, learning and development. We're looking to eradicate Sunday Blues from our team’s vocabulary.

The Role

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.

The success of our business, and our clients’ businesses, is built around the impact of our team’s work, and we’re committed to providing an environment where you can continue to grow, take ownership, and flourish.

What will you be doing?

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. You’ll have opportunities to contribute ideas, influence technical decisions, and support the growth of the team.

Your core responsibilities will include:

• 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.
• Upholding rigorous QA standards by following internal and client processes, maintaining documentation, and ensuring flawless delivery.
• 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.
• Keeping up to date with platform updates, new feature releases, and changes in CRO tooling, ensuring our clients benefit from the latest capabilities.
• Providing mentorship and support to junior developers, sharing knowledge and fostering a culture of continuous improvement.

What are we looking for?

• At least 2 years of hands-on experience in Conversion Rate Optimization (CRO) development and experimentation.
• 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 personalization platforms (e.g., AB Tasty, Optimizely, VWO, Webtrends Optimize).
• Proven ability to design, implement, and troubleshoot technical solutions for experiments.
• Strong problem-solving skills, attention to detail, and ability to manage multiple projects simultaneously.
• Excellent communication skills, with the ability to explain technical concepts clearly to both technical and non-technical stakeholders.

Nice-to-have skills:

• Familiarity with backend technologies and API integrations.
• Hands-on experience with analytics tools (e.g., Google Analytics, GA4, Adobe Analytics).
• Understanding of SEO principles, performance optimisation, and accessibility standards.
• Previous experience mentoring or supporting junior developers.
• A proactive approach to learning, innovation, and continuous improvement.

Perks of the job

• Salary of £40-50k
• 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
• Work from anywhere for up to four weeks a 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.
• Strengthen your mental well-being through our partnership with OpenUp giving you access to personalised support from certified psychologists and lifestyle experts.
• Make a difference with contributions to charity. Hookflash will match all staff charitable donations made throughout the year, supporting the causes you care about.
• We have plenty of opportunities for development and growth. We have always found the more rewarding approach to scaling the team is through developing the people we have, whether the person is securing their first job or more experienced heads. We want to support you in your career goals because if you’re happy and successful, we’ll be happy and successful.
• What else do you want? 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.