Product Engineer (Frontend Leaning - React / TypeScript)

About MarvelX

MarvelX builds specialized AI agents for complex and highly regulated domains such as insurance claims, compliance, and enterprise support. Our systems run in real world environments where accuracy, reliability, and clarity matter. The market is enormous and we are growing quickly.

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. We do not split work across a backend team and a frontend team that throw it over a wall.

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, and it is a senior one.

The role

We have no designer, and we are not planning to hire one soon. You will be the person who decides how MarvelX looks and feels: what a claims handler sees first, how dense a screen can get before it stops being readable, what an empty state says, what happens when the agent is wrong. You design in code, put it in front of users, and change it.

Our users are claims handlers who spend their day reviewing what an AI agent did and deciding whether to trust it. The agent streams its work, revises what it already said, and is sometimes confidently wrong. Making that calm and legible is the job.

You also build with coding agents every day, and you are the one who makes agent-written frontend code good. Agents produce competent, generic UI in one prompt. Getting from there to something a user trusts is judgement, and we want the person who has it.

What you will work on

• Own the interfaces our customers use all day: review queues, evidence views, dense forms and tables where a wrong click costs money

• Make the design calls: layout, hierarchy, interaction, copy, loading and failure states

• Build interfaces for AI output: streaming, revisions, confidence, citations back to the source, and a clear line between what the agent did and what the human decided

• Build and own the component library and design system, so the good version is the default for everyone else

• Set up how we build frontend with agents: repo rules, skills, visual and test checks that catch what the agent gets wrong before a human has to

• Build the backend slice behind your interface in Python and FastAPI, and own the API contract

• Keep it fast and accessible, measured rather than assumed

What you bring

• Four or more years building production React and TypeScript, full-time, with at least one product used by real customers whose interface you owned end to end

• Taste you can defend: you can say why a screen works, and you can show us screens you made

• You notice when something feels off, and you say so, including to the founders

• Deep React: rendering, state, what re-renders under a stream and why

• You build with coding agents daily and have your own setup around them: rules files, skills, subagents, checks. You own what ships, whoever typed it

• You can tell when a layout is wrong and why, whoever wrote the CSS, and you think in systems for spacing, type, colour and motion

• You go into the backend when the feature needs it, without waiting for someone else

• Product sense: you start from the user and the outcome

• Testing instincts: you write the test that fails when the important thing breaks

Show us your work

Use the "Cover Letter, public artifacts, stories" field in the application to link something you built: a live product, a repo, a design system, a short screen recording. One interface you made tells us more than a list of frameworks. If your best work sits behind a company login, screenshots and a few sentences on what you owned are fine.

Bonus points for

• Real-time and streaming UIs (WebSocket, SSE)

• Data-dense B2B tools: tables, review queues, role-based views

• Interaction and motion design

• Having owned a design system that other engineers built on

• BYOC / on-prem products

• Startup experience

Location & eligibility

Based in Amsterdam, at least 3 days a week in the office. Work eligibility in the Netherlands required; we are not able to sponsor visas in the Netherlands yet.