Billet
CLI tool · AI engineering
A terminal AI coding agent built from scratch on the raw Anthropic SDK. Includes the agentic loop, tool use, sandboxing, and skills.
Built with TypeScript and Bun.
The source code is on GitHub.
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Hello. I am Stefan, a senior full-stack engineer with 30 years of professional experience, based in Berlin.
As a freelance developer I build applications with TypeScript, React, Node.js, and AI.
Experience
I have spent the last 10 years working with React, Node.js, and TypeScript for enterprise customers and startups. Before that, I have 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. I have coached individuals and teams. I am also a Certified Scrum Master.
In recent projects I have used agentic coding tools like Claude Code and Cursor.
Skills
TypeScript
React
Node.js
AI
Scrum
Customers
These are some customers I have worked for:
- Zalando
- O2
- HRS
- SAP
- Movinga
- Kühne + Nagel
- Reuters
- Fyber
- Postbank
- HERE
- Intersection
- Commerzbank
Testimonials
I have some customer testimonials on LinkedIn.
Portfolio
Here are some side projects I have worked on recently:
Recto
WEB APP · PRODUCT ENGINEERING
Every book designer who has built a page plan in InDesign knows the moment: you need to insert a page, and every following page tile has to be moved by hand, every page number updated, one by one. On a 600-page book, that is a lot of work.
“Every time I had to insert a page, I felt like crying.”
Simona, book designer
Many designers skip the page plan entirely and just hold the structure in their head, even though clients want one. I have built Recto to make it easier for designers.
Recto is a visual flat-plan tool for print designers that visualizes a publication the way books are actually made: As pages, spreads, and print sheets.
Built with React, TypeScript, React Router 7, and Supabase.
Smart Rename
macOS app · AI engineering
A macOS app that renames document filenames according to document contents. The app uses an LLM to read the document contents and generate a new filename.
Built with Tauri, React, TypeScript, Rust, and the Vercel AI SDK.
Code
See some of my code on GitHub.
Availability
I am available as a contractor, remotely or in Berlin.
Contact me or check out my CV.