Freelance or permanent - Senior .NET Developer - Blazor UI (Blazor, UI focus)

Tasks and responsibilities

In a public-sector digital-services environment, you will develop secure, accessible and responsive business applications that support citizens, healthcare professionals and internal users in Belgium. You will work across the application stack, from the Blazor user interface to the .NET services behind it, while contributing to technical decisions and supporting colleagues.

You will join an ICT department of approximately 250 professionals working on more than 50 projects in different development phases. The organisation is modernising its application landscape towards a cloud-native architecture on Microsoft Azure, using Azure Service Bus and containerised workloads. A platform engineering team provides shared libraries, the design system, DevOps pipelines and standards for the application teams.

Web user interfaces are standardised on Blazor, allowing one .NET skill set to cover the complete application. The UI is the part of the application used by citizens, healthcare professionals and employees, so it must be accessible, consistent and responsive. The organisation is also exploring the responsible use of AI in business applications and software development.

Job purpose

As Senior .NET Developer with a UI focus, you will design, develop, integrate and maintain modern business applications. You will take ownership of their user interfaces while contributing to the underlying services. 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 operations.

You will translate functional and technical requirements into reusable, accessible solutions. Your work will support a consistent user experience across devices and browsers, correct integration with services and APIs, reuse of the shared component library and design system, and compliance with standards for architecture, security, quality, maintainability and delivery.

As a senior developer, you will help resolve complex technical issues, make well-founded design choices, improve engineering practices and support colleagues through coaching and code reviews. The role remains strongly hands-on, with direct contributions to feature development, testing, troubleshooting and continuous improvement across both the UI and its supporting services.

Key responsibilities

• Provide technical direction for Blazor development across teams and promote consistent UI architecture, reusable components, coding standards and engineering practices in line with the platform team's standards.
• Develop features, reusable components, prototypes, technical improvements and bug fixes using C#, modern .NET, Blazor, Razor components and the .NET Web APIs on which they depend.
• Design scalable, maintainable and reusable front-end structures that align with the organisation's architectural principles, and contribute to the shared component library built on MudBlazor and the shared design system.
• Build responsive 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. Consider usability, browser compatibility and the public-service context throughout the development process.
• Work with functional and business analysts and UX stakeholders to clarify requirements, assess feasibility and translate user and business needs into sound technical solutions.
• Integrate Blazor applications with REST APIs and JSON-based services, including typed clients, suitable error handling, state management, validation and resilience. Extend the Web APIs when a feature requires it.
• Implement secure authentication and authorisation flows using OAuth 2.0 and OpenID Connect for internal users, healthcare professionals and citizens, each with its own identity provider. Apply secure development practices throughout the application lifecycle.
• Maintain code quality through structured pull-request reviews, refactoring, SonarQube static analysis, coding standards and clear, reusable and testable components.
• Define and maintain unit tests, Blazor component tests with bUnit, service-level integration tests and, where appropriate, automated UI tests with Playwright. Follow the test pyramid to support reliable releases and prevent regressions.
• Use Git, Azure DevOps repositories, boards and CI/CD pipelines for controlled versioning, automated builds, testing and deployment to Azure environments.
• Select the appropriate Blazor render mode for each application, monitor and improve loading time, rendering behaviour and responsiveness, and use Dynatrace and browser tools to diagnose issues in test and production.
• Coach developers, share Blazor and accessibility expertise, document solutions and contribute to continuous technical improvement.
• Lead the analysis and resolution of complex end-to-end issues from the browser through the API to the database across development, test and production environments.
• Evaluate relevant .NET and web technologies and patterns, including AI-assisted development practices, and recommend adoption when they provide sustainable value and align with architectural and security decisions.

Key technical expertise

You should have recent, substantial hands-on experience in the following areas:

• C# and modern .NET: Advanced proficiency in C# and current .NET, including .NET 10 or later, asynchronous programming, dependency injection, clean code and maintainable application design.
• Blazor and Razor components: Recent 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. You understand prerendering, streaming rendering, component lifecycle, state handling, forms, validation and reusable component libraries such as MudBlazor.
• HTML, CSS and responsive design: Strong command of semantic HTML, modern CSS and responsive design for consistent use across devices and screen sizes.
• Accessibility: Practical experience delivering interfaces that meet WCAG 2.1 level AA, including keyboard navigation, screen-reader support, contrast, focus management and accessible forms. You are comfortable testing with assistive technologies.
• REST API integration and JSON exchanges: 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 with OAuth 2.0, OpenID Connect, JWT and claims-based authorisation.
• Data access: Working proficiency with Entity Framework Core and SQL, sufficient to implement features end to end and diagnose data-related issues.
• Testing: Strong experience with unit testing, Blazor component testing with bUnit and service-level integration testing. Automated UI testing with Playwright is an advantage. You can 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: A demonstrated focus on code quality, code reviews, application security, maintainability, observability and reusable components.
• AI-assisted development: Experience using GitHub Copilot, Claude Code or a similar coding assistant in a professional setting, with sound judgement about when to use these tools and how to review their output.
• JavaScript and 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 suitable patterns for component design, separation of concerns, state management, dependency management and scalable application structures.
• Performance and browser diagnostics: Experience analysing rendering, network calls, memory usage and client-side performance with browser development tools, together with an 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 for application delivery and troubleshooting.
• Distributed systems: Sufficient understanding of messaging, including Azure Service Bus and NServiceBus, and distributed systems to collaborate effectively with integration-focused colleagues and diagnose end-to-end issues.
• Additional ecosystem assets: Knowledge of SharePoint as a document management system or of legal document stores with WORM requirements is an asset where relevant to the assigned application domain.

Key soft skills

• Technical leadership and mentorship: Guide developers, provide constructive feedback, share knowledge and support professional growth while remaining hands-on.
• Collaboration: Work effectively with analysts, architects, UX stakeholders, security specialists, testers, platform engineering, operations and business representatives in a multidisciplinary public-service environment.
• Problem-solving and decision-making: Identify root causes, compare options, explain trade-offs and make pragmatic, sustainable technical decisions.
• User focus: Understand the needs of citizens, healthcare professionals and internal users, including users of assistive technologies, and translate them into clear, accessible and efficient digital experiences.
• Communication: Explain complex technical matters clearly to technical and non-technical stakeholders and produce concise, useful technical documentation.
• Resilience and adaptability: Manage changing technologies, priorities and requirements while maintaining quality, security and delivery commitments.
• Continuous improvement: Follow relevant developments in .NET, Blazor, web standards, accessibility, security and software engineering, and apply them with sound judgement.

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

You should be able to 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, particularly 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 with GitHub Copilot, Claude Code or a similar tool (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)

Your profile

Demonstrated experience as a front-end developer with a strong .NET and Blazor background.

Skills

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

Languages

• Dutch
• English
• French

Offer

You will be part of a growing Belgian SME where initiative and personal development are encouraged. We will provide you with an enjoyable work environment with fun colleagues. We will work out a career plan with you, with attention and a budget for extra education/certification. You can count on an attractive salary, supplemented with extra-legal benefits, including a company car.

(Freelance is also possible)