.NET developer (Mid – Senior)

Nion is an IT company, built through the successful consolidation of three well-established tech firms. Rooted in Stockholm, our mission is to drive innovation and deliver impactful digital solutions for a global client base spanning Sweden, Norway, the UK, Italy, and the US.

We thrive on complexity, simplifying challenges for major players across fintech, telecommunications, healthcare, logistics, etc.

Joining us means stepping into a culture where your voice matters, and your personal growth is matched by the diverse, high-impact projects you’ll work on.

At the moment we’re expanding our .NET Core team, so we’re looking for a .NET Developer, passionate about building high-quality, scalable backend systems. If you have a solid technical foundation, a curiosity for new technologies, and enjoy taking ownership of complex projects from concept to deployment, this opportunity might be for you.

Key responsibilities:

• Design, development, and maintenance of backend services using .NET technologies.

• Work extensively with RESTful APIs— ensuring stability, version compatibility, clear contracts, and reliability.

• Collaborate across multiple teams to align API contracts, versioning strategy, authentication flows, and reusable integration standards.

• Write clean, maintainable code with emphasis on performance, quality, observability, and engineering best practices

• Apply clean architecture principles and contribute to well-structured, modular solutions

• Investigate and debug issues across different environments and microservice interactions

• Support junior engineers through knowledge sharing and mentorship

• Communicate clearly with clients, technical leads, product owners, architects, and other engineering stakeholders

Required Qualifications:

• Minimum 5+ years professional experience with:

.NET technologies (ASP.NET Core, .NET Core, ASP.NET Web API)

• Strong C# proficiency and solid Git practices

• Experience with different ORMs (EF Core, NHibernate or dapper)

• Strong understanding of API integration principles, including versioning, pagination, error handling, and contract reliability

• Adherence to DRY, KISS, and SOLID principles in day-to-day development

• Modern authentication & authorization: OAuth2, OpenID Connect, tokens, scopes, claims

• Database experience: MSSQL, PostgreSQL, MongoDB

• Unit & integration testing: NUnit, xUnit (or similar)

• Awareness and understanding of different software architectures (layered, clean, hexagonal, microservices)

• Understanding of CI/CD pipelines, containerization (Docker), and cloud services (AWS/Azure/GCP)

• Excellent communication skills and strong ownership mindset

Additional Experience That’s a Plus:

• Message brokers: RabbitMQ / Azure Service Bus / Kafka

• Background processing: Hangfire, Quartz, Worker Services

• Some experience with frontend library

The Ideal Candidate Is:

• Highly Professional and committed to delivering solutions that meet client business needs.

• Reliable and takes full ownership of tasks, big or small.

• A great communicator and team player.

• Flexible and open to occasional travel as required by client projects.

Language:

• English: Fluent

How We Support You at Nion

At Nion, we don’t just offer a job — we offer a place where your growth, well-being, and success are at the center. What you’ll enjoy here:

• A collaborative, flat-structure environment where support is built in — your Consultant Manager acts as a dedicated mentor and “co-pilot,” ensuring your professional development and well-being are always on track.

• A high-trust culture that gives you autonomy, ownership, and the freedom to share and implement our ideas.

• Career development plan and continuous learning opportunities through hands-on projects, mentorship, and access to top learning resources.

• A vibrant culture where people genuinely enjoy working together, supported by strong team spirit, knowledge sharing, and fun social events.

Additional benefits:

• A hybrid work model and flexible working hours.

• Competitive salaries and regular performance reviews.

• Private health insurance.

• Company-sponsored mobile devices and paid subscriptions.

• Paid Fitness programs for diverse lifestyles.

Ready to take ownership of challenging projects and work with a team that truly has your back?