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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."

46  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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Legacy Modernization

AI

When Real-Time Payments Meet Thirty-Year-Old Code

Legacy banking infrastructure wasn't built for instant payments. AI-powered legacy code modernization can help—but only if you start now.

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Legacy Modernization

AI

When Legacy Infrastructure Meets Real-Time Demands: The Modernization Reckoning

Legacy systems weren't built for instant payments and AI workloads. Here's why AI-powered legacy code modernization is no longer optional.

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Legacy Modernization

AI

When Infrastructure Modernization Becomes the Strategy, Not the Detour

AI-powered legacy code modernization is no longer optional. Learn why enterprises treating infrastructure upgrades as strategy outperform those still calling it maintenance.

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Legacy Modernization

AI

Agentic Readiness: Why Your Portfolio Assessment Strategy Needs to Change Now

AI-powered legacy code modernization promises speed, but portfolio-scale agentic readiness demands more than tool selection. Here's what CTOs must assess first.

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Legacy Modernization

AI

Why Cloud Migration Certifications Mean Less Than You Think

AWS competency badges look impressive on vendor slides. But cloud-ready architecture modernization requires more than credentials - it demands understanding your specific legacy mess.

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Legacy Modernization

AI

Legacy Systems Are Not Technical Debt - They Are Your AI Advantage

Your legacy systems hold decades of business logic that AI needs to learn from. The question is not whether to replace them, but how to unlock their value.

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Legacy Modernization

AI

Why Legacy Scheduler Migrations Fail and What Actually Works

Legacy scheduler migrations fail because teams underestimate hidden dependencies. Learn how AI-powered legacy code modernization changes the approach.

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Legacy Modernization

AI

Modernizing Mission-Critical Systems Without Shutting Them Down

Legacy application modernization is hard. Doing it while keeping mission-critical systems running is harder. Here is how to approach the impossible.

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Legacy Modernization

AI

Composable Architecture Is Not a Silver Bullet - But It Might Be Your Only Way Forward

Composable architecture promises gradual legacy modernization without the big-bang rewrite. But the gap between the vendor pitch and your production reality is where projects go to die.

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Legacy Modernization

AI

Why Enterprise Java Migration Still Fails (And What Actually Works)

Most enterprise Java migration projects don't fail because of technology. They fail because no one asked the right questions before writing the first line of code.

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Legacy Modernization

AI

When Legacy Systems Cost More Than Crime: The Hidden Tax of Old Code

Legacy systems don't just slow you down. They stop you from doing your job. Here's what happens when outdated infrastructure meets mission-critical operations.

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Legacy Modernization

AI

When Modernization Means Rethinking, Not Replacing

Legacy modernization doesn't always mean ripping everything out. Sometimes the smartest path forward is understanding what you already have and surgically improving it.

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Legacy Modernization

AI

Why AI-Powered Legacy Code Modernization Is Different This Time

AI-powered legacy code modernization isn't just faster automation. It's a fundamentally different approach that changes who can modernize what, and when. Here's what actually works.

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Legacy Modernization

AI

When AI Rewrites Your Mainframe: The Promise and the Fine Print

AI-powered legacy code modernization promises to transform mainframe applications into cloud-native systems. But what actually happens when you let an algorithm reimagine decades of business logic?

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Legacy Modernization

AI

Why the Best Modernization Projects Don't Start With a Rip-and-Replace

America's largest banks are modernizing core systems without tearing everything down. Here's why the smartest CTOs are choosing surgical modernization over full rewrites.

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Legacy Modernization

AI

When AI Agents Start Rewriting Your Mainframe: What CTOs Actually Need to Know

AI agents now promise to modernize legacy code without human engineers. But can they really handle the messy, undocumented systems your company has run for decades?

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Legacy Modernization

AI

When Mainframes Move to the Cloud: The Legacy Connection Problem

Moving workloads off mainframes sounds simple until you realize the connections matter more than the code. Here's what enterprise leaders miss about legacy application modernization.

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Legacy Modernization

AI

When Moving to Cloud ERP Means Starting Over: The Hidden Reset

Cloud ERP migrations promise efficiency, but they often force teams to rebuild everything they spent years perfecting. Here's why your procurement pricing logic vanishes in the move.

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Legacy Modernization

AI

When Modernization Means Starting Over: What Nobody Tells You

Infrastructure modernization often requires dismantling the very systems that keep your organization running. Here's what happens when the price of progress is organizational disruption.

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Legacy Modernization

AI

AI-Powered Legacy Modernization: What Actually Works and What Doesn't

AI promises to modernize your legacy systems faster and cheaper than consulting firms. But most CTOs don't know where AI genuinely helps versus where it creates new problems.

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Legacy Modernization

AI

Why AI Agents Won't Fix Your Legacy Modernization Problem Alone

AI-powered legacy code modernization tools promise speed and automation, but without strategy and human judgment, they deliver refactored chaos instead of real transformation.

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Legacy Modernization

AI

Why Legacy System Modernization Fails: The Real Cost of Waiting

Most organizations know their legacy systems are holding them back. What they don't see is the compound interest on technical debt, calculated in opportunities missed while they wait for the "right time" to modernize.

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Legacy Modernization

AI

Legacy Modernization in 2028: What Southwest and IBM Just Taught Us

Southwest Airlines just committed to becoming fully cloud-based by 2028. IBM and ServiceNow are betting on AI-assisted legacy modernization. What do these moves tell us about the real cost of waiting?

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Legacy Modernization

AI

What Actually Drives Technology Modernization (And Why Security Is Finally Forcing the Issue)

Technology modernization isn't happening because of innovation. It's happening because security vulnerabilities, compliance mandates, and operational risk are forcing CTO decisions that should have been made years ago.

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Legacy Modernization

AI

Why Cloud Migration Without Modernization Is Just Expensive Lifting

Moving legacy systems to the cloud without addressing their architecture doesn't solve technical debt. It just relocates it at premium prices while creating new operational risks.

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Legacy Modernization

AI

What Technical Debt Is Actually Costing You (And Why the Number Is Bigger Than You Think)

Technical debt isn't just a developer problem. It's a business risk with a measurable price tag - and most CTOs are underestimating it badly.

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Legacy Modernization

AI

Application Modernization Services: The Definitive Guide for Enterprise Leaders

Application modernization services help enterprises transform legacy systems into scalable, cloud-ready platforms. Here is what every CTO needs to know before choosing a path.

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