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Claus Villumsen

Contributor

Contributor

I started my people management "career" when I became CTO of Bullguard Internet Security, which was mainly a development team based in Romania. The truth is, I didn't have anything but my common sense and determination to make good products that could guide me in my everyday people management. If I did well by "my guys", maybe it was blind, dumb luck. Sure, I read a couple of psychology and people management books, but I never found the recipe or how-to-guide to do right by people. I am not ashamed to brag about my most outstanding achievement in my professional life: "Making a shit load of people motivated to come to work."

19  articles by  Claus Villumsen

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Work

Productivity

11 Coding Habits That Make Engineers Effective at Legacy Modernization

Legacy modernization requires different instincts than greenfield development. These are the eleven habits that separate engineers who succeed at it from those who struggle.

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Productivity

You Chose to Build. Twenty Years Later, That Decision Is Still Running Your Business.

The build vs buy decision doesn't end when you ship. It continues every time you need to modernize what you built. Here is what happens when your custom system becomes your biggest constraint.

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Work

Digital Transformation Stalls When Legacy Systems Cannot Keep Up. Here Is the Fix.

Every digital transformation strategy eventually hits the same wall. The legacy system that cannot be modernized fast enough. Here is why that wall exists and what it actually takes to get through it.

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Team Management

You Inherited a System Built by a Team Nobody Can Find Anymore. Now What?

When an outsourced team hands over a system nobody fully understands, you have a legacy problem before the ink is dry. Here is how to take control of code you did not write.

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Productivity

Why Legacy Modernization Teams Work Better When They Think Differently

Legacy modernization is a deeply human problem. The systems we inherit were built by people with different assumptions and contexts. Understanding them requires the same diversity of perspective.

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Work

How We Built Four AI Agents to Convert Legacy HTML Into a Strapi CMS

We had a mountain of legacy HTML that needed to become structured Strapi CMS content. Manual conversion would have taken months. We built four AI agents to do it instead. Here is how they work.

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Productivity

AI

How Coinbase Could Have Avoided Years of Technical Debt

Coinbase built a Ruby on Rails monolith that scaled to billions in transactions and then became a liability. The technical debt they accumulated took years to address. Here is what the faster path looks like.

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Work

AI

How Wise Spent Five Years Migrating a Monolith — and What a Faster Path Looks Like

Wise built a smart monolith. It worked perfectly until it did not. The five-year migration that followed was painful and expensive. Here is what a different approach could have looked like.

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AI

Gartner Wants Intelligent Applications. Here Is How Legacy Systems Get There.

Gartner published a clear message in 2025. Legacy applications cannot support AI capabilities without transformation. Here is what that actually means and how you close the gap without a big-bang rewrite.

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AI

How We Squeezed a 1998 VBA Codebase Into One AI Agent
*Not by force. Not by throwing money at the problem. By going back to the basics of real engineering — washing code until it was clean enough for a machine to understand.*
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Legacy Modernization

AI

Your Best Developer Is Working on the Wrong Thing
Most companies think they need more developers. They don't. They're wasting the ones they already have. A CTO's honest look at the allocation problem hiding inside most engineering teams — and what application modernization actually changes.
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AI

AI vs. Consulting for Legacy Modernization: An Honest CTO's Guide
You have a legacy system holding your business hostage. A consulting firm costs a fortune. AI tooling sounds risky. An honest CTO’s guide to what each approach actually delivers — and how to combine them without getting burned.
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AI

How to Assess and Roadmap a Large Legacy Estate: A CTO's Field Guide
Someone handed you a list of 23 legacy systems and said “make a plan.” No documentation, no ownership map, no clear budget. This is the practical field guide for how CTOs actually assess a large legacy estate and build a modernization roadmap that gets funded and executed.
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Legacy Modernization

AI

Regression-Safe AI Refactoring: Why Faster Is Only Better If Nothing Breaks
AI can refactor your legacy codebase fast. But speed that silently breaks billing logic, compliance rules, or downstream dependencies is not an advantage. This is the practical governance model — characterization tests, scope discipline, canary rollouts — that makes AI refactoring trustworthy.
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AI

The Continuous Modernization Pipeline: How to Keep Modernizing Without Stopping to Ship
Most modernization programs stall because they are designed as projects with a start and end date. The organizations winning in 2026 treat modernization as a permanent pipeline — embedded in every sprint, measured like delivery, and impossible to pause without also pausing shipping.
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AI

Legacy Modernization

When AI Modernization Is Overkill — and When It Isn't
The most trusted thing a vendor can say is: this is not the right tool for you. Honest fit criteria for when AI-assisted legacy modernization is genuinely the right call — and when a simpler, cheaper approach will produce better outcomes.
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Legacy Modernization

AI

CAST, vFunction, GitHub, and Kodebaze: Choosing the Right Legacy Modernization Platform
CAST, vFunction, GitHub Copilot, OpenRewrite, Kodebaze — they keep appearing in the same conversations but they are not competing for the same job. An honest map of what each platform does well, where it runs out of road, and how to build the modernization stack that matches your actual problem.
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AI

Legacy Modernization

The Monster in the Basement

A Norwegian vehicle leasing company. A 1998 Access database with VBA forms. Twenty-five Italian engineers with a plan I knew would fail. And me, saying yes before I understood what I was getting into. This is what happened next.

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Cross-Platform Development

AI

We Use GitHub Copilot Every Day. Here's Why We Don't Use It to Modernize Legacy Code.
Every developer on our team has GitHub Copilot open. We use it every day. But when we pointed it at a 750,000-line VBA codebase from 1998, it was confident, fast, and wrong in ways that were hard to spot. Here is what we learned.
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