Senior .NET Developer (VB.NET / ASP.NET) – Web & Legacy Systems

Salary: Salary Negotiable, based on experience

About the role

We're looking for a hands-on Senior .NET Developer. You'll own our ASP.NET web applications and the legacy systems behind them. Over time, you'll help us add AI-enabled features. Our applications run on ASP.NET (.NET Framework 4.8) with VB.NET code-behind. They talk to other systems through simple XML-over-HTTP web services. You'll report directly to the Technical Director and work with a stable codebase that has real users depending on it, so the emphasis is on understanding it deeply, improving it thoughtfully, and modernising where it adds value rather than rewriting for its own sake. Our primary language is VB.NET. If you're a strong C# developer who is happy to work in VB.NET, we'd like to hear from you — the transition is straightforward and we'll support it.

Key responsibilities

• Maintain, enhance and troubleshoot ASP.NET / .NET Framework 4.8 web applications
• Investigate and resolve production issues across the application, IIS and Windows Server
• Develop and maintain XML-over-HTTP web services and integrations with external systems
• Support our legacy applications (VB6 desktop applications) — full internal training provided
• Design and integrate AI-enabled features using LLM APIs, prompt design and tool/function calling

About you

• 5+ years' commercial development experience, mainly on Microsoft/.NET technologies
• Strong ASP.NET, VB.NET (or C# with willingness to learn VB.NET) and Visual Studio
• JavaScript, jQuery, Bootstrap, HTML and CSS
• HTTP-based web services, XML and JSON
• IIS and Windows Server administration for application deployment and troubleshooting
• Some exposure to VB6 — you won't be writing new VB6 applications, but you will need to be comfortable reading and debugging legacy VB6 code when issues arise (training provided)
• Experience owning production issues on business-critical applications
• Strong debugging and analytical skills, and the ability to work independently in an established codebase
• Comfortable learning unfamiliar and legacy technologies
• A genuine interest in a long-term role and in applying Generative AI to existing business applications

Benefits

• Permanent, long-term position with a stable, established business
• 2–3 days work from home per week
• Internal training on our legacy systems and on AI development
• Direct access to the Technical Director and genuine ownership of your work
• Occasional on-call for production issues — in practice this is extremely rare

About us

We are an established software company of 20–30 people. We build tools that let developers create web applications on various database platforms, and we maintain a suite of established, business-critical web and legacy applications for our customers.