Founding Frontend Engineer (+ Equity) at Mozart AI

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 Founding Frontend Engineer Salary Not Disclosed Company Description Mozart AI is a $7M+ funded London startup backed by Balderton Capital and Kevin Hartz, transforming music creation into a social, effortless experience. We are building the future of music production with a WASM audio engine and real-time collaboration tools for everyone from grandmas to Grammy winners. Job Description As the Founding Frontend Engineer, you will own the "backend of the frontend" for a million-line React codebase. You'll architect high-performance SSR systems, scale state management, and build agent-ready UI infrastructure. This is a high-ownership role for a specialist-generalist who values velocity, product taste, and defining the future of music. Location London, UK Why this role is remarkable Work directly with the founders to own the end-to-end architecture, state, and delivery for a revolutionary social music product.Backed by $7M+ from elite investors including Balderton Capital (backers of Revolut) and Kevin Hartz (founder of Eventbrite).Tackle extreme engineering challenges like a WASM audio engine, 60fps WebGL rendering, and real-time multiplayer collaboration. What You Will Do Master the 1M+ line React codebase to own the TanStack Start and SSR architecture, streaming, and caching strategies.Consolidate client state management and harden UI/state separation to ensure a thin, predictable wrapper over backend APIs.Build agent-native infrastructure, ensuring all UI actions are accessible to AI agents through decorators and semantic code paths. The ideal candidate Deep React expertise with production SSR experience and a proven ability to architect large-scale, high-performance web applications.AI-native workflow where agents are your primary tool for refactors and building automated verification systems and E2E tests.Strong product taste with an interest in music creation and the ability to work in-office 5 days a week in London. 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.