Exem monitors electromagnetic fields across France — radio, cellular, every operator. Cities and local authorities rely on its tools for public-health transparency: measured waves, network coverage, 3D antenna projections, and the administrative paperwork that follows them. That offer lived in a handful of small, inconsistent apps; this project merges it into one coherent web application — site-planning tools, cartography layers, clustered measurement points and data-exploration panels, all on the same interactive map.

I built it from scratch as the sole front-end in a two-person product team. Under the map work, the foundation is a Storybook-driven component library — 100+ components implemented from the Figma designs, each built skeleton-first, so loading states are a property of the system rather than an afterthought. API types are generated from the OpenAPI specs, so the front-end cannot drift from the backend contract; i18n was in from day one.

Stack bets: TanStack Start over an ever-heavier Next.js, and React Strict DOM — close to the DOM and accessible by default, while keeping the cross-platform door open. A budget cut ended the mission before launch; the front-end was handed over near-complete to Exem's in-house team.