About Chaïm
Chaïm Zonnenberg
.NET developer with 20+ years of experience. I help .NET teams accelerate with agentic coding, without review chaos or mounting technical debt. Also specialised in Identity/SSO.
.NET developer with 20+ years of experience. I help .NET teams accelerate with agentic coding, without review chaos or mounting technical debt. Also specialised in Identity/SSO.
I'm Chaïm, 44 years old, married and father of two. I live in De Bilt near Utrecht, The Netherlands. When I'm not behind my screen, I enjoy hiking and playing board games with the kids.
What drives me? Complex problems. Genuinely, they make my day. When everyone says "that's too complicated" or "we don't have people for that", that's when the light goes on for me. I can't sit still as long as there's something left to solve.
I've been programming since I was seven. At sixteen, I sold my first software product to 35 customers. That combination of building and entrepreneurship never left.
After two cum laude bachelor's degrees (Computer Science and Mathematics), I completed my master's in Computer Science (specialisation Game and Media Technology) at Utrecht University. Since then, I've been building software for enterprise organisations: from financial institutions to real estate and pension management.
In 20+ years of enterprise software, I've learned that the hardest problems are rarely purely technical. It comes down to building the right thing at the moment it matters, alongside people who actually know the domain. That's what I'm good at.
years of enterprise software experience
paying customers on own SaaS products
enterprise organisations served
"Chaïm got up to speed exceptionally fast and consistently made the right decisions based on his deep knowledge of .NET and SQL Server."
Cees, Software Architect at multinational
These are the patterns I see in the .NET world, and in my own daily practice:
"Copilot is switched on, but nothing changes. Some developers are enthusiastic, others want nothing to do with it. We have no shared way of working and no agreements."
"Our enterprise client demands SSO and SCIM. The deal is under pressure. Every week of delay costs us trust, and possibly the contract."
"We need a senior developer who hits the ground running. Not someone who needs three months to understand the codebase, while the roadmap is screaming for results."
"Our technical debt keeps growing. Every sprint we push the complex problems to next time. Surely we shouldn't keep kicking the can down the road forever?"
I recognise that pressure. At ABN AMRO, PGGM and Van Lanschot I've seen from the inside how teams struggle with missing specialist knowledge. It doesn't have to be that way. With the right person on board, you can achieve in weeks what otherwise takes months.
At seven, we had a Microsoft MSX computer at home. Not to play games. I wanted to understand how it worked. A year later I was writing my first programs. At sixteen, I sold software to 35 customers. Building and entrepreneurship were in my DNA from the start.
After two cum laude bachelor's degrees and a master's in Computer Science (Utrecht University), I started at DTZ Zadelhoff, where I quickly grew from developer to data manager. Then came Kadenza, where I worked on complex valuation models.
In 2011 I went freelance. It was never about earning more. I wanted to pick the problems I work on myself. Since then I've taken on major assignments at ABN AMRO, PGGM and Van Lanschot, as developer, architect and project manager. The complex, specialist challenges where teams get stuck, that's what drives me.
In 2019 I built Factuur-Assist.nl, an invoicing platform that now has 135+ paying customers. No side project. It proves I can build, launch and keep complete products running for years.
Since August 2025 I build daily with Claude Code, the same tools I'd bring to your team. This website? Built with it. I use daily what I'd set up with you.
Is your team stuck on AI, SSO, or complex .NET features? For SSO and complex .NET problems, I've likely solved this kind of thing before. For AI workflow, I bring daily hands-on practice.
"Chaïm is a true professional. One you don't want to let go from day one. Proactive is his motto. He picks up what matters and doesn't let go until it's resolved."
Robert, IT Team Lead at financial institution
Tell me about your situation. I'll give you an honest assessment: whether I'm the right person, and how I'd approach it.