Senior Frontend Engineer - Design Systems

"We may say most aptly that the Analytical Engine weaves algebraic patterns just as the Jacquard loom weaves flowers and leaves." — Ada Lovelace, 1843 What Lovelace saw in the loom was the pattern — flowers and leaves, repeated faithfully, each one begun by a hand that chose it. Mercury is built from patterns too. Every component, every interaction our customers come to trust, starts with someone deciding how it should go, and making it good enough to be used again and again. Tending those patterns, and giving everyone at Mercury the means to weave with them, is the work of our Design System team, and the north star of this role. As a Senior Frontend Engineer on the Design Systems team, you will build and care for those patterns: the components and foundations that everything else at Mercury is built on. Done well, a single decision here makes every product team faster. The ground under that work is shifting, though. Software is being built in new ways, and AI is increasingly part of how design systems are made and used. We are looking for someone who is fluent at that intersection: deeply versed in design systems, and equally as serious about what it takes to build a system that holds up at the leading edge of AI. As part of this role, you will: Build and maintain the components, patterns, and foundations (tokens, type, color, layout) that Mercury's product is woven from, holding a high bar for accessibility, performance, and pixel-level craft. Work hand-in-hand with design partners to bring new patterns from concept to production, tightening the loop between ideation and what actually ships. Lead projects that ship new UI patterns to solve real pain points for product teams, helping them build better experiences faster. Develop a design system that's as ready for AI as it is for people, applying the technology to create leveraged outcomes. Invest in the design system's prototyping experience, shaping the next iteration of how our design function rapidly prototypes, iterates on the product, and explores new concepts. Raise the craft and AI fluency of the people around you, through mentorship and clear best practices. The ideal candidate for the role: We're look ing for someone who cares about the foundational work that lets other people do their best work, and who's eager to help define what a design system means in a world where agents build alongside us. A successful candidate will likely have: 4+ years of frontend development, with deep experience in React, TypeScript, and modern web technologies.