Senior UI Engineer

About StackOne: StackOne is the AI Integration Gateway for SaaS products and AI Agents. Backed by GV and Workday Ventures ($24M raised), we help builders of SaaS platforms and AI Agents orchestrate hundreds of scalable, accurate, and enterprise-grade integrations. Our platform combines 25,000 pre-mapped actions on 200 connectors, an AI-powered integration development toolkit, plus security by design: a real-time architecture, managed authentication and permissions, and end-to-end observability. Join us on our fast trajectory to build the future of agentic integrations. WHY THIS ROLE EXISTS StackOne’s product experience is our brand. As our first dedicated UX Engineer you will be the in-house authority on taste, polish, and performance. You will own the component library, shape our micro-frontend architecture, and ensure that every pixel, motion, and millisecond of latency makes customers feel like they’re using the best-engineered platform on the market. WHAT YOU’LL DO - 80 % Front-end craft & design systems - 20 % API-aware performance engineering - Collaborate with our Designer to define & steward our design system – set the visual language, build reusable primitives, and maintain libraries that power every StackOne user interfaces. - Ship pixel-perfect UIs – React (primarily) plus; own theming, performance, and thoughtful motion. - Make performance a feature – instrument Core Web Vitals, budget bundle sizes, optimise hydration patterns, and chase performance where it matters. - Provide and maintain internal tooling as well as AI rules to allow every technical team to contribute to the front-end while aligning with the best practices you will help set. - Prototype & validate – turn product ideas into interactive proofs-of-concept that help PMs and designers converge on the right solution fast. - Champion taste & detail – host design-quality critiques, stamp out visual debt, and be the go-to voice when “good enough” isn’t. WHAT YOU’LL BRING MUST-HAVES - 4+ yrs prof