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

• Collaborative and supportive project environment

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