Move your legacy .NET application to .NET 10 without a big-bang rewrite
I map what your old system really does, pin that behaviour down with automated tests, then let AI agents do the heavy rewriting while I review every change. You get a working slice in weeks and a costed plan for the rest.
Tell me about your system
Framework version, rough size, what worries you most. I reply within one working day.
Does this sound like your system?
Most legacy applications still work. The problem is what it costs to change them, staff them and keep them safe.
The support clock is running
Unsupported software keeps running. It just stops getting security fixes, which is what auditors, insurers and enterprise customers ask about.
Reach end of support. After that, no more security fixes from Microsoft.
Microsoft sourceExtended support has ended. Security updates now need paid ESUs.
Microsoft sourceExtended support ends. Many legacy IIS apps still run on it.
Microsoft sourceStill patched with Windows, but Windows-only and feature-frozen. WebForms and WCF server have no direct successor in modern .NET.
Microsoft sourceHow an AI-assisted migration works
AI writes code fast. It does not know what your system is supposed to do. The method exists to close that gap.
Map
AI-assisted analysis of the whole codebase: every screen, endpoint, stored procedure and integration, plus the business rules hidden inside them. You get a map your team can read.
Pin down
Characterisation tests record what the old system does today, input by input. The new system is checked against that record automatically, so nothing changes by accident.
Migrate in slices
Old and new run side by side behind a proxy and traffic moves one module at a time. AI agents write most of the code; I review every pull request before it merges.
Harden and hand over
Security review, CI/CD, logging and monitoring, then documentation and a walkthrough. Your team owns the result.
What I modernise
| From | To |
|---|---|
| ASP.NET WebForms | ASP.NET Core with Razor Pages, Blazor or React |
| WCF services | REST or gRPC on ASP.NET Core (CoreWCF as a bridge where clients can't change yet) |
| ASP.NET MVC 5 / Web API 2 | ASP.NET Core on .NET 10 |
| WinForms / WPF on .NET Framework | .NET 10 desktop, or a web front end where it pays off |
| VB6 and VB.NET | C# on .NET 10, with the business rules carried over and proven by tests |
| Classic ASP | ASP.NET Core on .NET 10 |
| Access databases and Excel-macro tools | A secure web application on SQL Server or Azure SQL |
| SQL Server 2012–2016 on Windows Server | SQL Server 2022 or Azure SQL, containers or Azure App Service |
Start small, decide with evidence
Each step is useful on its own, and you can stop after any of them. I run at most two modernisation projects at a time, so I can review every change myself.
15-minute call
Tell us what the system does and what is hurting. If a rewrite is the right move, you get a written proposal for the Blueprint.
- ✓No preparation needed
- ✓A straight answer on fit
Modernisation Blueprint
I analyse your code under NDA and migrate one real screen or service, so the plan is based on evidence from your codebase.
- ✓Inventory of screens, services, data and integrations
- ✓Risk register: hidden business logic, dead code, security gaps
- ✓One migrated screen or service with passing characterisation tests
- ✓Target architecture on .NET 10
- ✓A fixed price for the full rewrite
Fixed-price rewrite
Module by module, old and new side by side. Each milestone is accepted when the new code passes the tests recorded against your current system.
- ✓Priced as a package, paid in milestones
- ✓No hourly or day-rate billing
- ✓On-site in the UK or remote, as the project needs
Modernisation Care
Keeps the system current after the migration so you never end up here again.
- ✓Each .NET LTS upgrade done for you
- ✓Dependency and vulnerability patching
- ✓An architect on call for your team
Who does the work
I’m Jan Sevcik, a software architect with 22 years in enterprise .NET. Before SelectWise I worked on legacy .NET modernisation and security compliance at MSD Animal Health, led a multi-system modernisation programme across 20 countries for Loomis, and spent nearly four years on the architecture of Saga’s membership platform.
My migration toolkit is a set of specialised AI agents for code analysis, test generation and review, built and refined on real .NET codebases. MSc in Software Engineering, Microsoft Certified Azure Solutions Architect Expert.
Frequently asked questions
Can AI really migrate a legacy .NET application?
AI agents now write most of the new code in a migration, quickly and well. They cannot tell you what the old system is supposed to do. That is why every engagement starts by recording the current behaviour in automated tests, and why I review every change the agents make before it is merged.
How long does a migration take?
The Blueprint takes two weeks. A full migration depends on size: a 50,000-line line-of-business app is usually a matter of months, a 500,000-line system closer to a year. AI shortens the coding; testing, data migration and user sign-off still run at human speed. The Blueprint ends with a fixed price and a timeline for your system.
Do we have to freeze development while you migrate?
No. I use the strangler fig pattern: old and new versions run side by side behind a proxy, and traffic moves to the new code one module at a time. Your team keeps shipping fixes to the old system until each module is switched over.
Is our source code safe?
I sign an NDA before seeing any code. The AI tools I use run under business terms that exclude training on your code, and if you prefer, the whole migration can run inside your own Azure or on-premises environment.
Should we move to .NET 10 or wait for .NET 11?
.NET 10 is the current long-term support release, supported until November 2028. .NET 11 is a standard-term release. For a business application, target .NET 10 now; the jump from 10 to the next LTS is a routine upgrade once you are off .NET Framework.
Our developers have GitHub Copilot. Is that not enough?
Copilot and Claude are part of how we deliver. Moving WebForms, WCF services or VB code is a rewrite with no one-click path, and the hard part is discovering and proving the business rules buried in the old system. That is the work we take on, as a fixed-price package. If your team wants to build the skills too, the team workshops cover the same method.
What about VB6, classic ASP or Access applications?
Those can be modernised too, usually into a C# web application on .NET 10 with a proper database. The Blueprint tells you whether a straight port or a rebuild of selected parts is cheaper.
What does it cost?
Everything is a fixed-price package; nothing is billed by the hour or the day. The Blueprint starts from £20,000 for two weeks and ends with a fixed price for the full rewrite, which is paid in milestones.
Find out what your migration really involves
A 15-minute call to see whether a fixed-price rewrite is the right move for your system.
Book a 15-minute callFurther reading: the AI migration reality check