Senior Frontend Engineer

About Arlequin

Arlequin is building the sovereign European alternative to Palantir: an AI platform capable of processing massive data volumes without bias, with high-impact use cases such as fighting disinformation. Founded in late 2024 by Hugo Micheron (researcher in geopolitics and systemic risk) and Antoine Jardin (CNRS research engineer).

~30 people, post-seed, Series A in progress. On-site in Paris.

The role

You’ll own the quality and consistency of the user experience across the HUDEX platform — analysis interfaces, complex data visualizations (knowledge graphs, time series, narrative dynamics), user journeys for creating projects and data collections. Our users are non-technical analysts handling massive datasets and AI outputs: interface quality is one of the key factors that makes the difference between contracts that renew and those that don’t. Your business impact is direct.

You’ll work hand in hand with product and a future senior Product Designer, represent the frontend voice in architecture decisions alongside the Head of Engineering, and progressively take ownership of the design system and cross-product patterns.

Stack

• Core : React 19, TypeScript, Tanstack Router + Query

• UI & styling: Mantine, Vanilla Extract

• Visualization: @observablehq/plot, d3, in-house graph library

• i18n : react-intl + FormatJS, workflow English/French

• Build: Vite, Turbo monorepo

• Backend interfacing: Hono, Drizzle, OpenAuth

• Quality: ESLint, Prettier, Jest, strict TS

What we’re looking for

• 5+ years of frontend experience, including at least 2 on data-driven products or complex interfaces

• Strong command of React and its modern ecosystem

• Real product and UX sensitivity — able to challenge a design to make it better

• Experience with data visualization (D3, graph libraries, Plot, or equivalent)

• Professional English

Bonus

• Ownership of, or significant contribution to, a design system

• Early/mid-stage startup experience

• Mastery of agentic coding tools and code models

• Interest in emerging tools and paradigms

Process (~2 weeks)

1. Screening (15 min)

2. Fit interview (30 min)

3. Technical interview (1h)

4. Founder culture fit (45 min)

5. Reference calls

6. Offer

Package

• 70-90k€ + BSPCE

• On-site central Paris