About MarvelX

MarvelX is building highly specialized AI agents for the most complex, heavily regulated industries. Think insurance claims, compliance, support. Automated by AI that actually works in the real world. The opportunity is massive, and we’re moving fast.

We hire Product Engineers, not narrow specialists. You own features end to end: the services and data behind them, the interface in front of them, and the product decisions in between. You will work directly with the founders and engineering leads to shape the systems and surfaces our customers rely on every day. We do not split work across a backend team and a frontend team that throw it over a wall. Everyone here ships across the stack and reasons about the whole product.

This is not a maintenance role. It is a chance to shape a product at an early and meaningful stage. We work on-site in Amsterdam three or more days a week.

Every Product Engineer at MarvelX is fullstack with a lean. This role leans frontend.

Where you will spend most of your time

You will own the user-facing surfaces that make our AI agents usable, reliable, and clear. You will turn complex AI behavior into interfaces that feel calm and trustworthy for users in regulated industries. You will still build and reason about the backend slice that feeds your interface and define the API contracts with the team, but the center of gravity is the frontend.

What you will work on

• Design and build user-facing features in React and TypeScript

• Create responsive, accessible UIs that hold up against real production data

• Build real-time interfaces for streaming AI output (WebSocket, SSE)

• Build the backend slice that feeds your interface, in Python and FastAPI, with the team

• Integrate with backend APIs, handling loading, error, and optimistic update states cleanly

• Diagnose and fix performance issues, perceived and measured (LCP, TTI, bundle size)

• Contribute to or help establish the component library and design system

What you bring

• Two to five years building production React applications with TypeScript

• Deep understanding of React patterns, hooks, rendering lifecycle, and state management

• Strong CSS skills (Tailwind, CSS-in-JS, or strong vanilla CSS) and responsive design instincts

• Comfort owning a feature end to end, including the backend slice that supports it

• Willingness and ability to work across the stack, backend included, when the feature needs it

• Product sense: you reason about the user and the outcome, not only the code

• Strong testing instincts (unit, integration, E2E)

Bonus points for

• Real-time / streaming UI experience (WebSocket, SSE, live dashboards)

• Experience building UIs for B2B / enterprise customers (data tables, role-based views, multi-tenant dashboards)

• Component library or design system contribution

• BYOC / on-prem product experience (offline-capable UIs, environment-specific config)

• Previous startup experience and comfort in fast moving environments

If you are excited by owning real interfaces end to end and putting AI into the hands of users in regulated industries, we would love to meet you.