HTML/CSS Developer

HTML/CSS - Senior Developers - AI Training - UK

About Prolific

Prolific is not just another player in the AI space – we are building the biggest pool of quality human data in the world.

Over 35,000 AI developers, researchers, and organizations use Prolific to gather data from paid study participants with a wide variety of experiences, knowledge, and skills.

The role

We're looking for Senior HTML/CSS Developers to join our Expert Network to help train and evaluate cutting-edge AI models. If you have a background in Software Engineering or Frontend Development, we'll send you a quick 10- to 15-minute test to assess your skills. If successful, you'll be invited to join Prolific as a participant, where you'll get paid to help AI understand and produce high-quality frontend code and design implementation.

Researchers looking for your skills tend to pay up to $40/hr, depending on skills and experience. You must be prepared to complete paid tasks that require one hour of uninterrupted work, though many are shorter.

What you’ll bring

• Educational Background: a BSc or higher in Computer Science, Software Engineering, Web Development, or a closely related technical field.
• Professional Experience: real-world experience as a Senior Frontend Developer or UI Engineer specialising in HTML/CSS.
• Coding Proficiency: ability to independently build complex, responsive layouts and components without relying on frameworks or libraries.
• Deep Domain Knowledge: expert understanding of the CSS cascade, specificity, the box model, Flexbox, CSS Grid, accessibility standards (WCAG), and cross-browser compatibility.
• Code Quality: a high standard for clean, semantic markup and maintainable CSS, including adherence to BEM methodology, design tokens, and modern CSS standards.

What you’ll be doing in the role

• Evaluate Code Accuracy: review AI-generated HTML/CSS for functional correctness, semantic structure, and adherence to best practices.
• Validate Logic & Reasoning: audit the step-by-step explanations provided by AI for layout solutions and styling approaches to ensure they are technically sound.
• Conduct Execution Testing: render model-generated markup and stylesheets in appropriate environments to verify visual output and cross-browser behaviour.
• Annotate Model Performance: identify areas where a model produces inaccessible markup, inefficient selectors, deprecated attributes, or hallucinated CSS properties.