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Damien Mercier

Damien Mercier · Freelance Product Engineer · France

I build digital products from idea to production.

Freelance Product Engineer specialising in React, Next.js and TypeScript. I help founders and product teams design, build and ship fast, reliable web applications.

Start a projectView my work

What I do

Problems I can take off your plate

Product development
From idea to production-ready product. I help scope, design and build features that solve a real problem, then ship them.
Frontend engineering
Fast, accessible and maintainable React applications, with a design eye and attention to the details users actually feel.
Backend & APIs
Reliable APIs, integrations and data flows. I work across the stack so features don’t stop at the browser.
Performance
Profiling, optimisation, caching and Core Web Vitals. I find why an app is slow and fix the causes, not the symptoms.
Product engineering
I work across product, design and engineering to ship useful features. I ask why before writing how.

React · Next.js · TypeScript · Node.js · Postgres · Supabase · Anthropic API · n8n

Selected work

Case studies, not screenshots

Flexiwork

Product and technical consulting on a B2B office-space platform: discovery, a 4-track roadmap formalised in a PRD, and an AI workflow that took a 45-minute sales task down to 30 seconds.

Product & Technical Consultant (freelance), returning client

Next.jsAnthropic APIn8nHubSpot

Campus Coach

Frontend engineer in a 7-person team on a B2C coaching platform with 40,000+ paying users: monetization flows, internationalization and new product verticals.

Frontend Engineer (freelance), 7-person frontend team

ReactTypeScripti18n

gPulse

Worked on Greenworking's employee-listening platform: automated the report chain that turns survey data into client decks, and built the React dashboards consultants use alongside it.

Full-stack developer, working directly with consultants and analysts

ReactData visualizationPowerPoint automation

WebGL lab

An ongoing playground for Three.js, React Three Fiber and Blender, exploring what it takes to ship performant 3D on the web.

Personal lab · ongoing

Three.jsReact Three FiberBlenderVite
All work

Background

Real product work, verifiable code

Experience

I am product and technical consultant for Flexiwork, a B2B office-space platform that brought me back four years after a first mission: discovery, a roadmap formalised in a PRD, and an AI workflow that cut a 45-minute sales task to 30 seconds. Before that I spent nearly two years as a frontend engineer on Campus Coach, a B2C coaching platform with more than 40,000 paying users, where I shipped the monetization flows and worked on the internationalization that opened the English-speaking market.

Verify for yourself

My code is on GitHub. References from people I have worked with are available on request: just ask.

Writing

Notes on building products

All articles

Have a product to build or improve? Let’s talk.

Tell me about your product and where it needs to go. I usually reply within one or two business days.

Start a projectdamien.mercier@me.com