Marcel Köhler
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Open for one side project

Frontend engineer with a design system habit.

Over fifteen years in development — a long fullstack stretch first, frontend by choice since. During that time I have gained a lot of experience in the development of simple websites and complex web applications.

15+
Years building
B.Sc.
Applied CS
Marcel Köhler
Senior Frontend Engineer“If you're doing something the same way you have been doing it for ten years, the chances are you are doing it wrong.”Charles Kettering

Flagship, 2021 to today

Marigold

Reservix' open-source design system, built on React Aria and Tailwind. I drive its development, maintenance and rollout across product teams — components, tokens, docs, adoption.

  • React
  • TypeScript
  • Tailwind
  • React Aria
View the system

More work

2021 to 2026

Something new

Coming soon

In the workshop for 2027 — a small product of my own, built on the stack below. Ask me about it.

TBA
2027

Mechadex

A small formation generator for the auto-battler game ‘Mechabellum’. It is designed to help players get started with the game and recommends suitable countermeasures depending on the opponent’s units.

Vite, Tailwind, React
2026

Kleine Welten Raak

Marketing site for a miniature-worlds studio — static, fast, owner-editable.

Next.js, TS, Tailwind
2025

Design Patterns in React

A working catalogue of the patterns behind component libraries.

Vite, TS, Tailwind
2024
3 of 7 projects shown

Experience

Reservix GmbH

2021 to Present

Senior Frontend Engineer

  • Part of the first fully agentic team developing AI-augmented workflows, including an MCP server that makes Marigold agent-readable and AI-assisted UI quality assurance.
  • Member of the front-end development management team at Marigold, the company design system used internally and by external product teams.
  • Build and maintain the Reservix webshop platform with PHP and the Symfony framework.

CG Car-Garantie Versicherungs AG

2009 to 2021

Fullstack Developer

  • Mentored and trained apprentices and students in software development.
  • Designed and developed Java web applications with Java EE and Spring Boot.
  • Built and maintained web applications in ColdFusion supporting core warranty and insurance processes.
  • Developed and maintained business-critical applications on the IBM System i (AS/400) platform.

Toolbox

  • Design systemsMarigold

    The company design system I lead — React Aria under the hood, Tailwind on top, used internally and by external product teams.

    MarigoldReact AriaMaterial UI

  • Frontend coreReact, TypeScript, Tailwind

    My daily surface: typed React components, file-based routing, utility CSS and a build that stays out of the way.

    React.jsNext.jsTypeScriptTailwindCSSViteHTML5CSS3

  • Testing, docs & QAVitest, Playwright, Storybook

    A design system is only trustworthy once proven: unit tests, real-browser flows, visual review on every pull request, and docs people actually open.

    VitestPlaywrightJestStorybookChromaticCypress

  • AI & agentsMCP, agentic workflows

    Part of the first fully agentic team at Reservix — I built an MCP server that makes Marigold agent-readable and use AI for UI quality assurance.

    Model Context ProtocolClaude

  • Backend & platformPHP, Symfony, Node.js

    The fullstack years still pay off: I keep the Reservix webshop platform running on PHP and Symfony, and I am comfortable anywhere in the stack.

    PHPSymfonyNode.jsMongoDBFirebaseDockerKotlinRaspberry Pi