Senior Software .NET Engineer (B2B)

Responsibilities

• Drive the modernization of an established, business-critical payment platform, migrating a large ASP.NET (WebForms/MVC) monolith from .NET Framework 4.x to .NET 8, together with its database layer and system integrations, in an on-premise environment.
• Combine deep .NET craftsmanship with modern, AI-assisted ways of working to make the migration faster and safer.
• Analyze the legacy codebase and shape an incremental, low-risk migration path module by module, with no big-bang rewrites.
• Design and implement the migration of application components from .NET Framework 4.x / ASP.NET (WebForms, MVC) to .NET 8 / ASP.NET Core.
• Refactor code toward SOLID principles and clean architecture as part of the migration.
• Modernize the Microsoft SQL Server data layer and the platform's integrations with surrounding systems.
• Use AI-assisted development tools, such as GitHub Copilot and LLM-based tooling, to accelerate legacy code analysis, refactoring, and test generation; help the team adopt these practices responsibly.
• Build automated unit and integration test coverage to verify the migration at every step.
• Collaborate with development teams and stakeholders on scope, sequencing, and technical decisions.
• Mentor less experienced developers and share modernization knowledge across the team.

Qualifications

• Successfully completed university degree in computer science or a comparable field of study.
• 6+ years of commercial software development experience.
• Extensive experience with C# and .NET across generations: .NET Framework 4.x with ASP.NET WebForms/MVC, and modern .NET 6/8 with ASP.NET Core.
• Hands-on experience modernizing or migrating legacy applications, including re-platforming, incremental refactoring, or strangler-fig-style approaches.
• Strong knowledge of software design principles and patterns, including SOLID and clean architecture.
• Solid experience with Microsoft SQL Server and data-layer refactoring.
• Practical daily experience with AI-assisted development, such as GitHub Copilot or similar LLM-based tools.
• Experience with automated unit and integration testing.
• Fluency in Polish and very good communication in English.
• Availability to work in a hybrid mode; remote workers are invited to the office once every month.