Senior UI Engineer

This is a job that Jill, our AI Recruiter, is recruiting for on behalf of one of our customers. She will pick the best candidates from Jack's network. The next step is to speak to Jack. Job Title Senior UI Engineer Salary Not Disclosed Company Description StackOne is a $24M Series A London startup building an AI Integration Gateway for SaaS platforms and AI Agents, backed by GV (Google Ventures) and Workday Ventures. Job Description As StackOne’s first dedicated UI Engineer, you will be the authority on craft, polish, and performance. You’ll own the component library, shape micro-frontend architecture, and ensure every pixel reflects best-in-class engineering. Working alongside founders from Google and Microsoft, you’ll build the infrastructure layer that enables the next generation of agentic integrations. Location London, UK Why this role is remarkable Join as the first dedicated UI/UX engineer, owning the entire front-end surface and setting the visual standards for a high-growth infrastructure platform.High-caliber environment backed by $24M from GV and Workday Ventures, founded by veterans from Google and Microsoft who value engineering taste and autonomy.Tackle unique performance challenges at the intersection of AI and enterprise integrations, building a system that orchestrates thousands of actions across hundreds of connectors. What You Will Do Lead the development and stewardship of StackOne’s design system, establishing the visual language, reusable primitives, and performance standards for all user interfaces.Ship high-fidelity, pixel-perfect UIs using React and TypeScript, while managing micro-frontend patterns and optimizing Core Web Vitals to ensure industry-leading latency.Collaborate with product and design teams to prototype interactive proofs-of-concept, while providing internal tooling and AI rules to help other engineering teams contribute. The ideal candidate 4+ years of professional front-end engineering experience with a deep focus on visual craft, design systems, and building production-scale React applications.Expert-level command of TypeScript, CSS fluency (Tailwind), and modern browser APIs, with a proven track record of migrating or scaling component libraries.Strong performance engineering instincts, including experience with monorepo tooling like NX or Turborepo and the ability to optimize backend bottlenecks impacting the client. Who are Jack & Jill? Ok, I'll go first. I'm Jack, an AI that gets to know you on a quick call, learning what you're great at and what you want from your career. Then I help you land your dream job by finding unmissable opportunities as they come up, supporting you with applications, interview prep, and moral support. And I'm Jill, an AI Recruiter who talks to companies to understand who they're looking to hire. Then I recruit from Jack's network, making an introduction when I spot an excellent candidate. How does this work? Jack's an AI agent for job searching and career coaching. He works for you.Jill is the AI recruiter working for the company. She recruits from Jack's network.If it's a match and the company wants to meet you, they'll make the intro. In the meantime, if you'd like, Jack will send you excellent alternatives. We never post fake jobs This isn't a trick. This is an open role that Jill is currently recruiting for from Jack's network. Sometimes Jill's clients ask her to anonymize their jobs when she advertises them, which means she can't share all the details in the job description. We appreciate this can make them look a bit suspect, but there isn't much we can do about it. Give Jack a spin! You could land this role. If not, most people find him incredibly helpful with their job search, and we're giving his services away for free.