Good Software Is a Door That Just Opens.
Hello. I am Stefan, a senior full-stack engineer with 30 years of professional experience, based in Berlin.
Together with product and design, I figure out what to build, then build it end to end: data model, API, and UI.
- Available
- Remote or Berlin
- German / English
Experience
I have spent the last 10 years working with React, Node.js, and TypeScript for enterprise customers and startups. Before that, I worked with C++, Java, and Ruby on Rails for 20 years.
In my 30 years of professional experience I have co-founded two companies, worked as a CTO, team lead, and lead developer, and have written two books about Java. As a co-founder I shaped the product as well as the technology; as a contractor I work closely with product owners and designers to decide what to build. I have coached individuals and teams. I am also a Certified Scrum Master.
How I Work
I practice agentic engineering, mainly with Claude Code: I set the architecture, agents implement, I review what ships, and automated tests keep the code reliable. I used this approach in production at Parloa and on my side projects, including my own coding agent, Billet.
Stack
- TypeScript
- React
- Node.js
- NestJS
- PostgreSQL
- MySQL
Customers
These are some customers I have worked for:
Selected Client Work
Parloa – AI-based contact center platform, Berlin. (2025)
I designed and built a server-driven UI package that lets backend developers ship service UIs without waiting on the frontend team. Built primarily with agentic AI, in a ten-person platform team.
Next Logistics Ventures – seabo – SaaS marketplace for chartering cargo ships. (2022–2024)
Lead full-stack developer. The product ran on a legacy PHP backend that had become the bottleneck for development. Rather than rewrite it, we added a second backend in TypeScript and NestJS and built new features there. I proposed both, ran the evaluation, and led a team of frontend and full-stack developers. I designed the data model for my own features and reviewed everyone else’s, and built the vessel database and Stripe subscription billing from scoping with the project manager to data model, API, and UI.
Zalando – procurement platform for €1 billion in annual fashion purchases. (2019–2020)
Helped scope the product with the product owner, then led greenfield frontend development: selected technologies, designed the architecture, and coached four developers in a cross-functional team of twelve.
More on the CV.
Testimonials
“Wir haben mit Stefan langfristig bei der Entwicklung eines neuen digitalen Produkts zusammengearbeitet. Stefan kann ich wärmstens empfehlen, sein fundiertes technisches Knowhow und seine ruhige Art haben das Team und das Produkt weit nach vorne gebracht. Insofern: bis zum nächsten Mal! :)”
“Right from the start, Stefan got involved in architectural design, helping make technology decisions, but also forming the team’s ways of working. He was active in mentoring some of our junior team members […] and was able to bring them to a level of independence in a short period of time. […] I would not hesitate to contract Stefan again, should the need arise.”
“Ich habe über 4 Jahre hinweg mit Stefan zusammengearbeitet. Er hat ein tiefes Verständnis für Softwarearchitektur. Bei den agilen Bedürfnissen eines Startups hatte Stefan stets das passende Konzept parat. […] Ich kann Stefan ohne Vorbehalte weiterempfehlen!”
See also LinkedIn.
Things I've Built
Here are some side projects I have worked on recently:
Billet (2026)
CLI coding agent built directly on the Anthropic SDK: agentic loop, bash and text editor tools, sandboxing, plan mode, skills, eval suite (TypeScript, Bun)
Smart Rename (2025)
AI-based desktop app that extracts invoice metadata and auto-renames files (Vercel AI SDK, Evalite, Tauri, TypeScript, React)
Recto (2026)
Published web tool for planning book page layouts, in production use on a 400-page book project (TypeScript, React, Supabase)
