Senior .NET Developer (Blazor, UI focus)

NIHDI context of work: Build the future of public health technology at NIHDI as a Senior .NET Developer with a user-interface focus. Your work will directly support digital services that contribute to the health and wellbeing of millions of people in Belgium. You will design and deliver secure, accessible, responsive and high-impact business applications end to end, from the Blazor user interface to the .NET services behind it, while guiding colleagues and contributing to sound technical decisions.

You will join an ICT department of approximately 250 professionals, actively engaged in more than 50 projects across different phases of development. NIHDI is transforming its application landscape toward a modern, cloud-native architecture on Microsoft Azure, using Azure Service Bus and containerised workloads to improve the way systems are built, integrated and scaled. A Platform Engineering team provides the shared libraries, the design system, the DevOps pipelines and the standards that every application team builds on.

NIHDI standardised its web user interfaces on Blazor so that one .NET skill set covers the whole application. The user interface is therefore not a separate discipline: it is the part of the .NET application that faces citizens, healthcare professionals and NIHDI employees, and it has to be accessible, consistent and fast. This transformation also includes the responsible integration of AI into business applications and into the way we develop them.

Join NIHDI to build smart, secure and purpose-driven digital services, and help shape the future of public health technology.

Job purpose: 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 NIHDI 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: Provide technical direction for Blazor development across teams and promote a consistent approach to UI architecture, reusable components, coding standards and engineering practices. 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. 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 NIHDI design system.

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. Collaborate with functional and business analysts and UX stakeholders to clarify requirements, assess feasibility and translate user and business needs into robust technical solutions. Integrate Blazor applications with REST APIs and JSON-based services, including typed clients, appropriate error handling, state management, validation and resilience.

Implement secure authentication and authorisation flows using OAuth 2.0 and OpenID Connect for the three audiences NIHDI serves. 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. Define and maintain unit tests, Blazor component tests (bUnit), service-level integration tests and, where appropriate, automated UI tests (Playwright).

Use Git, Azure DevOps repositories, boards and CI/CD pipelines to support controlled versioning, automated builds, testing and deployment to the Azure environments. 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. Coach developers, share Blazor and accessibility expertise, document solutions and contribute to a culture of technical excellence.

Lead the analysis and resolution of complex end-to-end issues, from the browser to the API and the database. Assess relevant .NET and web technologies and patterns, including AI-assisted development practices, and recommend adoption when they add sustainable value.

Key technical expertise: The developer should demonstrate recent, substantial hands-on experience in C# and modern .NET (advanced proficiency, including asynchronous programming, dependency injection, clean code), Blazor and Razor components (production-grade applications, render modes, prerendering, streaming rendering, component lifecycle, state handling, forms, validation, reusable component libraries such as MudBlazor), HTML/CSS and responsive design, accessibility (WCAG 2.1 AA), REST API integration and JSON exchanges, OAuth 2.0 and OpenID Connect, Entity Framework Core and SQL, testing (unit, component, integration, UI automation), Git/Azure DevOps/CI/CD, engineering quality and security, AI-assisted development, JavaScript/TypeScript interoperability, front-end architecture and design patterns, performance and browser diagnostics, cloud and containerised environments, distributed systems awareness, and NIHDI ecosystem assets (SharePoint, legal document stores).

Key soft skills: Technical leadership and mentorship, collaboration, problem-solving and decision-making, user focus, communication, resilience and adaptability, continuous improvement. Language proficiency: mastery of French or Dutch and professional proficiency in English are required; passive understanding of the second national language is an asset.

Expected seniority: The role requires a developer who can work autonomously on complex application challenges, take ownership from requirements through production support, influence technical choices, and raise the quality and consistency of the wider development team, in particular on the user-interface side. Seniority must be demonstrated through recent hands-on delivery, not only through coordination or advisory experience.

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).