Backend Developer

Requirements

• Strong experience with C# and ASP.NET Core
• Commercial experience with .NET (preferably .NET 8+)
• Experience in modernizing legacy applications (ASP.NET Framework 4.8 / WebForms / WCF) and migrating them to modern architectures (.NET 10)
• Solid experience in designing and building REST APIs and service-based architectures (API-first, domain-driven design)
• Good knowledge of MS SQL Server / Azure SQL
• Hands-on experience with Microsoft Azure, especially:

- Web Apps

- Container Apps

- Service Bus

- Key Vault

• Strong analytical skills and ability to work independently
• Team player with experience working in an Agile / Scrum environment
• Proactive mindset with a focus on continuous improvement and system modernization
• Fluent English (spoken and written)

Nice to have:

• Experience with Docker (containerization) is a strong plus
• Experience in upgrading legacy systems
• React.js and experience in ERP environments

We are SIENN Living Online Technology! Let’s grow with us!
Do you want to be a part of something meaningful? We are working on an international project in the financial sector for a Dutch Client specializing in audits, accounting, payroll, HR, and tax advisory.

Project Information:
We are supporting the development and modernization of an existing accounting application.

Role:
As a Backend Developer, you will:

• Build and modernize backend services using ASP .NET Core MVC and .NET 8+
• Participate in migration to Microsoft Azure
• Ensure code quality and scalability
• Collaborate with international teams

Technology stack:

• ASP .Net Core MVC, .Net 10, C#
• Azure
• Entity Framework
• Docker
• Git, MS SQL Server

What we offer:

• B2B rate: 90 - 125 PLN/h
• Work in an international project environment
• Access to international training and certifications (e.g. Microsoft MCP)
• Opportunities for professional development and knowledge sharing
• Possibility to access optional benefit platforms (medical care, sports card, insurance, language courses)
• Collaborative and supportive project environment

Requirements: .NET, Domain-driven design, MS SQL Server, Azure SQL, C#, Service Bus, .NET Framework, REST API, Docker, WCF, Vault, Analytical skills Additionally: Sport subscription, Training budget, Private healthcare, Flat structure, International projects, Ubezpieczenie na życie, Bike parking, Free coffee, Free snacks, Free lunch, Free parking, Modern office.