About this Senior UI Engineer role at StackOne
About StackOne
StackOne is the integration infrastructure for AI agents. Backed by GV and Workday Ventures ($24M raised), we make it possible for any AI agent — whether our customers build it into their product or buy it off the shelf — to take real action across the enterprise stack. Our platform gives agents 430+ connectors and 26,000+ pre-built actions, an AI connector builder for everything not covered yet, and the production layer agents actually need: semantic tool discovery that cuts token use by up to 80%, managed authentication and per-action permissions, the most accurate prompt injection defense on the market, 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 professional front-end engineering with a portfolio that focus on the details.
React & TypeScript at production scale; comfortable with hooks, suspense, and server components.
Deep CSS fluency (Tailwind or equivalent) and experience of modern browser APIs.
Proven track record building or migrating component libraries/design systems.
Strong performance tuning instincts: Lighthouse, Core Web Vitals, bundle analysis, code-splitting.
Familiarity with monorepo tooling (NX or Turborepo) and micro-frontend patterns.
Ability to dive into back-end code (Node, React-router, sveltekit) to remove perf bottlenecks, instrument metrics, or adjust API shape.
Nice-to-haves
Svelte, Web Components, or other framework experimentation.
Experience with auth flows (OAuth2, OpenID Connect) and secure front-end patterns.
Web Motion & animation chops
Prior work on B2B developer tools or dashboards at seed-to-Series-B stage.
Why Join Us?
Meaningful share options (EMI) - share in the company's success as we grow
25 days holiday + 1 additional day per year of tenure
Private health insurance - including dental & optical
£15/day lunch budget when working from our London office, up to £120/month
£1,000 for your home office set up + £500/year top-up
Annual team offsite to sunny spots (last ones were in Spain and Portugal ☀️)
Join one of Europe’s fastest-growing startups
Work with a veteran team of ex-employees of Google, Microsoft, Oracle, Coinbase, JP Morgan and more
Health, fitness and gift card discounts
Cycle2Work and Electric Cars scheme
Hybrid work set up - typically 2 days in the office
Ready to help us change the game for SaaS integrations? Get in touch and let's chat!
We believe diversity drives innovation. We encourage individuals from all backgrounds to apply. As an equal-opportunity employer, we celebrate diversity and are committed to creating an inclusive environment for all employees.
