Senior .NET Developer

The Senior .NET Developer (Blazor, UI focus) is responsible for the design, development, integration and maintenance of modern business applications within NIHDI's application landscape, with particular ownership of their user interfaces. The role combines advanced hands-on development with technical leadership, coaching and close collaboration with analysts, architects, UX stakeholders, security specialists, the Platform Engineering team and operational teams.
The developer translates functional and technical requirements into robust, reusable and accessible solutions. The role ensures that applications provide a consistent and accessible user experience across devices and browsers, integrate correctly with our services and APIs, reuse the shared component library and design system, and comply with organisational standards for architecture, security, quality, maintainability and delivery.
As a senior member of the development team, the developer helps resolve complex technical challenges, makes well-founded design choices, improves engineering practices and supports other developers through coaching and code reviews. The role remains strongly hands-on and contributes directly to feature development, testing, troubleshooting and continuous improvement, on the user interface as well as on the services it depends on.

Key responsibilities

• Technical leadership for the user interface: Provide technical direction for Blazor development across teams and promote a consistent approach to UI architecture, reusable components, coding standards and engineering practices, in line with the Platform Engineering team's standards.
• Hands-on development: Dedicate a significant part of the role to developing features, reusable components, prototypes, technical improvements and bug fixes using C#, modern .NET, Blazor and Razor components, and the .NET Web APIs they rely on.
• UI architecture and component design: Design scalable, maintainable and reusable front-end structures that align with NIHDI architectural principles, and contribute to the shared component library built on MudBlazor and the our design system.
• Accessibility and responsive design: Build responsive user interfaces with semantic HTML and modern CSS that meet WCAG 2.1 level AA, as required of Belgian public bodies under the European Web Accessibility Directive, and take account of usability, browser compatibility and our public-service context.

Requirements analysis: Collaborate with functional and business analysts and UX stakeholders to clarify requirements, assess feasibility and translate user and business needs into robust technical solutions.
API integration: Integrate Blazor applications with REST APIs and JSON-based services, including typed clients, appropriate error handling, state management, validation and resilience; extend the Web APIs when a feature requires it.
Authentication and application security: Implement secure authentication and authorisation flows using OAuth 2.0 and OpenID Connect for the three audiences NIHDI serves (internal users, healthcare professionals and citizens, each with its own identity provider), and apply secure development practices throughout the application lifecycle.
Code quality and reviews: Ensure high code quality through structured pull-request reviews, refactoring, static analysis with SonarQube, coding standards and the development of clear, reusable and testable components.
Testing and quality assurance: Define and maintain unit tests, Blazor component tests (bUnit), service-level integration tests and, where appropriate, automated UI tests (Playwright) to support reliable releases and prevent regressions, following the test pyramid.
DevOps and delivery: Use Git, Azure DevOps repositories, boards and CI/CD pipelines to support controlled versioning, automated builds, testing and deployment to the Azure environments.
Performance and observability: Choose the right Blazor render mode for each application, monitor and improve loading time, rendering behaviour and responsiveness, and use Dynatrace and browser tooling to diagnose issues in test and production.
Coaching and knowledge sharing: Coach developers, share Blazor and accessibility expertise, document solutions and contribute to a culture of technical excellence and continuous learning.
Troubleshooting and support: Lead the analysis and resolution of complex end-to-end issues, from the browser to the API and the database, across development, test and production environments.
Technology evaluation: Assess relevant .NET and web technologies and patterns, including AI-assisted development practices, and recommend adoption when they add sustainable value and align with NIHDI architectural and security decisions.
 

Key technical expertise
The Senior .NET Developer (Blazor, UI focus) should demonstrate recent, substantial hands-on experience in the following areas:

• C# and modern .NET: Advanced proficiency in C# and current .NET (.NET 10 or later) development practices, including asynchronous programming, dependency injection, clean code and maintainable application design
• Blazor and Razor components: Recent hands-on experience developing production-grade Blazor applications, including the Blazor Web App model and its render modes (static server-side rendering, interactive Server, WebAssembly and Auto), prerendering and streaming rendering, component lifecycle, state handling, forms, validation and reusable component libraries such as MudBlazor.
• Accessibility: Practical experience delivering interfaces that meet WCAG 2.1 level AA: keyboard navigation, screen-reader support, contrast, focus management and accessible forms, including testing with assistive technologies.
• REST API integration and JSON exchanges: Proven experience consuming and building REST APIs with ASP.NET Core, handling JSON exchanges and implementing robust validation, error handling and integration patterns.
• OAuth 2.0 and OpenID Connect: Practical experience implementing secure authentication and authorisation in web applications using OAuth 2.0, OpenID Connect, JWT and claims-based authorisation.
• Data access: Working proficiency with Entity Framework Core and SQL, sufficient to implement a feature end to end and to diagnose data-related issues.
• Testing: Strong experience with unit testing, Blazor component testing (bUnit), service-level integration testing and, ideally, automated UI testing (Playwright). Able to design testable code and integrate automated tests into delivery pipelines.
• Git, Azure DevOps and CI/CD pipelines: Advanced use of Git, branching and pull-request workflows, Azure DevOps repositories and boards, and CI/CD pipelines for automated build, test and deployment.
• Engineering quality and security: Demonstrated focus on code quality, code reviews, application security, maintainability, observability and the development of reusable components.
• AI-assisted development: Experience using AI coding assistants (GitHub Copilot, Claude Code or similar) in a professional setting, with sound judgement about when to rely on them and how to review their output.
• JavaScript/TypeScript interoperability: Knowledge of JavaScript or TypeScript and JavaScript-Blazor interoperability is an asset, particularly when integrating browser APIs or specialised front-end libraries.
• Front-end architecture and design patterns: Ability to select and apply appropriate patterns for component design, separation of concerns, state management, dependency management and scalable application structure.
• Performance and browser diagnostics: Experience analysing rendering, network calls, memory usage and client-side performance using browser development tools, and understanding of the scalability characteristics of each Blazor render mode.
• Cloud and containerised environments: Working knowledge of Microsoft Azure and an understanding of containerised deployment relevant to application delivery and troubleshooting.
• Distributed systems awareness: Sufficient understanding of messaging (Azure Service Bus, NServiceBus) and distributed systems to collaborate effectively with integration-focused colleagues and diagnose end-to-end issues.

Required technical skills
C# (8 years)
Modern .NET / ASP.NET Core (6 years)
Blazor and Razor components, including Blazor Web App render modes (3 years)
HTML, CSS and responsive design (6 years)
Web accessibility, WCAG 2.1 AA (3 years)
REST APIs and JSON exchanges (6 years)
OAuth 2.0 and OpenID Connect, JWT, claims-based authorisation (5 years)
Entity Framework Core and SQL (5 years)
Testing: unit, component, integration and UI automation (6 years)
Git, Azure DevOps and CI/CD pipelines (6 years)
Agile / Scrum (8 years)
AI-assisted development (GitHub Copilot, Claude Code or similar) (1 year)

Assets
Microsoft Azure (3 years)
.NET Framework maintenance (2 years)
Azure Service Bus / NServiceBus (2 years)
JavaScript / TypeScript and JS interop (2 years)

Skills

1. Agile / Scrum
2. AI-assisted development (GitHub Copilot, Claude Code or similar)
3. Blazor and Razor components, including Blazor Web App render modes
4. C#
5. Entity Framework Core and SQL
6. Git, Azure DevOps and CI/CD pipelines
7. HTML, CSS and responsive design
8. Modern .NET / ASP.NET Core
9. OAuth 2.0 and OpenID Connect, JWT, claims-based authorisation
10. REST APIs and JSON exchanges
11. Testing: unit, component, integration and UI automation
12. Web accessibility, WCAG 2.1 AA

Languages
Dutch - Level Active knowledge
English
French - Level Active knowledge

Questions:
I agree to come and work at the office in Brussels at least 2x a week
I agree to telework within the Belgian borders