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.NET development – C#, ASP.NET Core and enterprise APIs

.NET development: C#, ASP.NET Core and enterprise applications

.NET development for scalable business apps, web APIs and Windows services – with ASP.NET Core, Entity Framework and clear integration architecture.

.NET Development

.NET – enterprise-ready and cloud-ready

With .NET and C# we build web APIs, portals and desktop components at home in Microsoft environments and hybrid cloud setups. ASP.NET Core delivers performance, structured DI and strong tooling.

We also support Delphi-to-.NET migrations and modernisation of older .NET Framework estates – with working intermediate releases instead of big-bang.

Technology overview: .NET Development — stack details and use cases on our technology page.

Our .NET services

From APIs to Windows services – typed and testable.

ASP.NET Core web APIs

REST and gRPC endpoints, authentication (Entra ID, JWT), versioning and integration into existing landscapes.

Enterprise & LOB apps

Forms, workflows, reporting and connection to SQL Server, PostgreSQL or existing ERP systems.

Migration & modernisation

Delphi, VB6 or .NET Framework lifted step by step to .NET 8/9 – including UI strategy (web vs desktop).

Azure & DevOps

App Service, containers, Key Vault, pipelines – operations with monitoring and clear runbooks.

C# & EF Core

Clean layers, migrations and unit tests with xUnit.

Security

OWASP-oriented APIs, secrets in vaults, regular updates.

Delphi migration

Experience modernising Delphi to .NET in mid-market companies.

Integration

ERP, finance interfaces and line-of-business connectors.

Frequently asked questions (FAQ)

  • When is .NET the right choice?
    For Microsoft stacks, strongly typed domains, enterprise policies or Delphi/VB6 estates targeting .NET. For pure content sites or AI backends we often evaluate PHP, Python or Node.js.
  • What does .NET development cost?
    Smaller APIs from around €18,000; larger LOB or migration programmes €50,000–150,000. Migration effort depends heavily on UI and data model.
  • Do you work with .NET Framework and .NET 8?
    Yes – we maintain Framework 4.x estates and build new work on .NET 8/9. Roadmaps show the gradual transition.
  • Cloud or on-premise?
    Both – Azure is common, but also IIS on-prem or Kubernetes. Decision based on compliance, latency and IT policy.
  • How does a Delphi-to-.NET migration work with you?
    Typically: estate review, target architecture (WinForms, WPF, Blazor), pilot module, then incremental domain migration with parallel operation. Details: /en/services/delphi-development/delphi-migration-dotnet and /en/services/legacy-modernization.
  • Do you use ASP.NET Core with Entra ID and JWT?
    Yes—authentication via Microsoft Entra ID, JWT for APIs and role-based authorization are standard. Hybrid scenarios exist for on-prem AD; we document identity flows for audit and operations.
  • Do you handle maintenance and releases after go-live?
    Yes—under retainer with SLAs, security patches and planned .NET upgrades. Alternatively handover with runbooks and team training. Many clients start with support and reduce external share gradually.
  • How do you test .NET APIs and desktop components?
    Unit tests (xUnit), integration tests against Testcontainers/SQL and—where useful—E2E for critical flows. CI pipelines block releases on red tests. More: /en/methodology/audit.

.NET in practice

We structure solutions in domain, application and infrastructure layers – testable without smart UI. Releases run through automated pipelines with quality gates.

  • Nullable reference types and analyzers in CI
  • Integration tests against Testcontainers/SQL
  • Structured logging (Serilog/OpenTelemetry)
  • API contracts documented for frontend teams

In the initial call we clarify estate, target architecture and a realistic migration or greenfield plan.

Related services

Scope: .NET for enterprise APIs

.NET development for ASP.NET Core APIs and Windows services in integrated estates—not every custom software topic (software development).

Contracts: API integration. Java alternative: Java development.

Related paths and adjacent topics

Service overview: Integration & interfaces (overview)

More integration & interface services

Adjacent service categories

Define the .NET assignment: new build, takeover or upgrade

A new build starts with the domain model, API contracts and permissions. A takeover starts with build reproducibility, dependencies, test coverage and secure access to repositories, databases and deployment. An upgrade begins with an estate review; we select the supported target version only after that review.

For APIs, we design authentication, authorisation, data access, error responses and idempotency with the connected systems. Complex contracts belong in API integration, while fundamental structure decisions belong in a software architecture review.

Handover includes reproducible builds, automated tests, documented configuration and an agreed rollback path. For Delphi estates, our Delphi-to-.NET migration service explains the dedicated migration route. Framework and version commitments follow code and dependency review.

Björn Groenewold

Up to 50% of your investment via BAFA/KfW

Use our funding calculator to see which government grants may apply to your project.

Björn Groenewold – Managing Director