Fulminous Software builds, modernises and supports Microsoft .NET applications for UK businesses: ASP.NET Core web apps and APIs, Azure cloud solutions, and migrations from ageing .NET Framework and Xamarin systems. You get secure, maintainable software, an itemised GBP quote and full ownership of the code.
- London-headquartered since 2019
- ASP.NET Core, Blazor, Azure, .NET MAUI
- NDA and full IP ownership
Modern .NET development for UK businesses
.NET is Microsoft's open-source platform for building web, cloud, desktop, and mobile applications in C#. It's fast, secure, and well supported, making it a popular choice for UK organisations in finance, healthcare, logistics, and the public sector. As a custom .NET development company, we help businesses build reliable, scalable applications tailored to their specific needs.
We develop new applications using the latest long-term support (LTS) releases and help businesses modernise existing .NET systems that are becoming harder to maintain. As a trusted custom .NET development company, our team covers design, development, testing, Azure deployment, and ongoing support.
Choosing the Right .NET Development Company?
Not sure what to look for when hiring a .NET development partner? Read our guide to learn how to evaluate technical expertise, project costs, security and ongoing support.
Our .NET development services
From new builds to legacy rescues, we cover the full .NET ecosystem, helping London businesses make informed decisions about hiring or outsourcing .NET developers in London based on their project requirements, budget and long-term goals.
Custom ASP.NET Core applications
Secure web applications, customer portals and internal tools built with ASP.NET Core and modern front ends.
APIs and microservices
REST and gRPC APIs and microservices that connect your systems and scale with demand.
Azure cloud development
Cloud-native .NET on Azure App Service, Functions, Azure SQL and Service Bus, with UK data regions.
Blazor front ends
Interactive web interfaces written in C#, sharing code and models with your .NET back end.
.NET MAUI apps
Cross-platform mobile and desktop apps for iOS, Android, Windows and macOS from one C# codebase.
Enterprise systems and integrations
CRM, ERP and workflow software integrated with Microsoft 365, Dynamics 365, SQL Server and third-party services.
Legacy .NET modernisation
Migrating .NET Framework, Web Forms, WCF and Xamarin applications to modern .NET.
DevOps and CI/CD
Automated builds, tests and deployments with Azure DevOps or GitHub Actions.
Support and maintenance
Security patching, version upgrades, monitoring and new features after launch.
Is your .NET application out of support?
Running unsupported versions means no security patches. This is where many UK systems stand today:
| If you're running | Support status | Recommended next step |
|---|---|---|
| .NET Framework (4.x) | Maintenance only, Windows-bound, no new features | Plan a staged migration to modern .NET |
| .NET Core 3.1, .NET 5, 6 or 7 | Out of support | Upgrade to .NET 10 as a priority |
| .NET 8 | Support ends November 2026 | Upgrade to .NET 10 now |
| .NET 10 | Current long-term support release | Keep patched and up to date |
| Xamarin | Support ended May 2024 | Migrate to .NET MAUI or another cross-platform framework |
Check Microsoft's official .NET support policy for the latest dates.
How we modernise .NET applications
Assessment
Review code, dependencies, hosting and blockers such as Web Forms or WCF.
Migration plan
Choose upgrade, re-platform or staged rebuild, with risks and costs clearly set out.
Test safety net
Add automated tests that capture today's behaviour before changing code.
Incremental migration
Move modules step by step so the business keeps running.
Cloud and go-live
Deploy to Azure or your servers, then monitor and optimise.
Planning a wider modernisation? See our legacy application modernisation services and cloud migration services.
Get a free .NET health check
Tell us about your application. We'll review its version, dependencies and risks, and recommend whether to upgrade, migrate or rebuild.
Why UK businesses choose .NET
Performance
Modern .NET is one of the fastest mainstream web frameworks, reducing hosting costs at scale.
Security
Built-in authentication, data protection and regular Microsoft security updates.
Microsoft ecosystem
Natural fit with Azure, Microsoft 365, Entra ID, SQL Server and Dynamics 365.
Long-term support
Predictable release cycle with long-term support versions for stable business systems.
Cross-platform
Runs on Windows, Linux and containers, and builds web, mobile and desktop apps.
Large talent pool
C# is widely used in the UK, making it easier to hire and maintain over time.
Technologies we use
| Area | Technologies |
|---|---|
| Back end | C#, ASP.NET Core, Web API, minimal APIs, gRPC, Entity Framework Core |
| Front end | Blazor, Razor Pages, MVC, plus React and Angular |
| Mobile and desktop | .NET MAUI, WPF, WinForms (for legacy support) |
| Databases | SQL Server, Azure SQL, PostgreSQL, Cosmos DB, Redis |
| Cloud and DevOps | Microsoft Azure, AWS, Docker, Kubernetes, Azure DevOps, GitHub Actions |
| Identity and integration | Microsoft Entra ID, OAuth 2.0, OpenID Connect, Microsoft Graph, Dynamics 365 |
Our .NET development process
Discovery
Goals, users, systems and constraints agreed up front.
Architecture
.NET version, hosting, data model, integrations and security approach.
Design
Wireframes and prototypes for key screens and journeys.
Development
Two-week sprints with working demos and code review.
Testing
Unit, integration, performance and security testing.
Deployment
Automated release to Azure, AWS or on-premises.
Support
Monitoring, patching, upgrades and new features.
.NET development cost in the UK
Indicative ranges. Your quote depends on scope, integrations, users and the condition of any existing code.
| Project type | Typical cost | Typical timeline |
|---|---|---|
| .NET version upgrade (modern .NET) | From £5,000 | 2 – 6 weeks |
| Focused business application | £15,000 – £40,000 | 8 – 16 weeks |
| Multi-user platform or portal | £40,000 – £120,000 | 4 – 7 months |
| .NET Framework migration or enterprise system | £50,000+ | Depends on size and condition |
Prices exclude VAT. For more detail, see our software development cost guide.
Ways to work with us
Fixed price
For a defined scope, such as a new application or a version upgrade.
Time and materials
For migrations and evolving requirements, with transparent billing.
Dedicated .NET developers
.NET developers working in your team on a monthly basis.
Business software from our portfolio
A selection of business platforms our team has designed and built.
Why choose Fulminous Software for .NET development
New builds and rescues
Equally comfortable starting fresh or untangling a legacy codebase.
Transparent GBP pricing
Itemised quotes with VAT shown separately.
Visible progress
Two-week sprints with working demos.
UK-hours collaboration
London-headquartered with project management during UK business hours.
Security built in
UK GDPR-aware design, secure authentication and regular patching.
You own the code
Full source code and documentation handed over.
.NET development FAQs
What does a .NET development company do?
A .NET development company designs, builds and maintains software using Microsoft's .NET platform and C#. That includes web applications with ASP.NET Core, APIs, cloud applications on Microsoft Azure, desktop and mobile apps with .NET MAUI, and modernisation of older .NET Framework systems.
How much does .NET development cost in the UK?
As a guide, a focused .NET business application typically costs £15,000 to £40,000, a multi-user platform £40,000 to £120,000, and complex enterprise systems more. Legacy migrations depend heavily on the size and condition of the existing code. We provide an itemised GBP quote after discovery.
Can you migrate our .NET Framework application to modern .NET?
Yes. We assess your existing .NET Framework application, identify blockers such as Web Forms, WCF or old third-party libraries, and migrate it to modern .NET in stages so the business keeps running. Migrating usually improves performance, security and hosting costs.
Our application runs on .NET 8. Do we need to upgrade?
Microsoft support for .NET 8 ends in November 2026, after which it stops receiving security updates. Most applications should plan an upgrade to .NET 10, the current long-term support release. Upgrades between modern .NET versions are usually far simpler than moving from .NET Framework.
We have a Xamarin app. What are our options?
Microsoft ended support for Xamarin in May 2024. The usual path is to migrate to .NET MAUI, which shares much of the same approach, or to rebuild in another cross-platform framework if that suits your roadmap better. We can assess your app and recommend the lowest-risk route.
Do you work with Microsoft Azure?
Yes. We build and deploy .NET applications on Azure using services such as App Service, Azure Functions, Azure SQL and Azure DevOps pipelines, with UK data regions available. We also deploy .NET applications to AWS and on-premises servers.
Can I hire dedicated .NET developers instead of outsourcing a project?
Yes. You can hire dedicated .NET developers who work in your team on a monthly basis, or have us deliver a complete project to an agreed scope.
Will we own the source code?
Yes. We sign an NDA before you share details, and full ownership of the source code, documentation and deployment configuration is transferred to you.
Let's talk about your .NET project
Whether it's a new build, an upgrade or a migration, tell us what you need. We'll come back with practical recommendations and an itemised GBP quote.
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