Prerequisites
Access to the repository and a test environment, build instructions, dependency versions and sample business workflows. If these are missing, reconstructing them becomes an explicitly scoped diagnostic task.
.NET / C# development
Freelance C# developer for your .NET software
20 years of intensive hands-on work with the Microsoft ecosystem. Robust business applications, high-performance backend services and user-friendly WPF interfaces — tailored to your business.
Independent developer based in Raismes, near Valenciennes — I work with companies in the Nord, the Hauts-de-France region and throughout France, on-site or remotely.
Engagement scope
Take over software and deliver a verifiable change.
An internal tool blocks your team, an API needs to evolve or a .NET Framework app has become hard to maintain? The first phase establishes how it actually works and isolates a useful change. Dependencies and available support determine the technical target.
Deliverables
Dependency and risk inventory, prioritised takeover plan, versioned code, tests for changed behaviour, deployment procedure and maintenance notes. A migration can be divided into phases with an identified rollback path.
Acceptance
Reproducible build, tests for the agreed scope and acceptance checks on scenarios defined with your users. During a takeover, critical workflows are checked before and after changes; remaining limitations outside scope are recorded.
Scoping and estimate
The quote follows a review of code, access and acceptance criteria. An audit may precede development when the starting point does not support a reliable estimate. Initial reply within 48 business hours.
Documented personal example: YouggyDrome, an ASP.NET Core facade shared by web and Flutter. The study explains the Navidrome boundary and the tests run. For a local business need, see scoping custom software in the Valenciennes area.
What I build
- Custom business applications and ERPs
- User-friendly, high-performance WPF interfaces
- Windows services and scheduled tasks
- REST APIs with ASP.NET Core
- ETL data integration: Semarchy xDI (formerly Stambia)
- Mirakl marketplace connectors for retail and e-commerce
- Migration from .NET Framework to .NET Core and legacy systems — see the .NET 8 to .NET 10 migration guide
- Reusable libraries and components
The stack
●C# 12+
●.NET
●WPF
●ASP.NET Core
●Entity Framework
●SQL Server
●Azure
●Semarchy xDI
●Mirakl
●xUnit / MSTest
Why C# / .NET?
A mature ecosystem with proven performance.
Robustness
Strong typing & testing
Static typing in C# helps detect errors early. Tests and code reviews build on that foundation to verify expected behaviour.
Performance
Ultra-fast .NET 8+
The latest versions of .NET are among the fastest runtimes on the market — ideal for high-load services.
Longevity
Planned maintenance
The target version and its support schedule are checked during scoping. Dependencies, documentation and tests then support maintenance and handover.
FAQ
Frequently asked questions about .NET development
What types of applications do you build in .NET/C#? +
I build custom business software (WPF, WinForms), Windows services, REST APIs with ASP.NET Core, desktop applications, data integration tools (ETL/Stambia) and migrations of legacy systems to modern architectures. For retail, I also work on freelance retail data integration: catalogue feeds, orders and marketplace connectors.
How long does a typical .NET project take? +
A module or feature generally takes 2 to 8 weeks. A complete piece of software can require 3 to 12 months depending on complexity. I start with a precise scoping phase to estimate the scope and timeline before any commitment.
Can you take over and evolve an existing C# project? +
Yes, it's a big part of what I do. I start with an audit of the existing code to identify the risks, technical debt and areas for improvement. I can then take over the project seamlessly, without starting from scratch.
Is .NET still relevant against newer technologies? +
.NET is one of the highest-performing runtimes on the market. Microsoft invests heavily in the platform, which now covers desktop, web, cloud, mobile and AI. It's a future-proof choice for strategic projects.