Hello. I am Stefan, a senior full-stack engineer with 30 years of professional experience, based in Berlin.

I work with product and design to figure out what to build, then build it end to end: data model, API, and UI.

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. 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.

In recent projects I have used agentic coding tools like Claude Code and Cursor.

Stack

TypeScript
React
Node.js
NestJS
PostgreSQL
MySQL

Customers

These are some customers I have worked for:

Zalando
Parloa
O₂
HRS
SAP
Movinga
Kühne+Nagel
Reuters
Fyber
Postbank
HERE
Intersection
Commerzbank

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.

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! :)
Timmo Köhler, CEO, Bitgrip

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.
Frieder Ulm, Team Lead at Zalando at the time

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!
Max Mayerhofer, Next Logistics Ventures

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)

Availability

I am available nowI am available as a contractor, remotely or in Berlin. I work in German or English.

Send me an email at post@stefanwille.com. Or check out my CV.