Senior .NET Developer (Legacy Specialist & AI Expert)

Responsibilities

• We move beyond traditional development by implementing repeatable, evidence-based SDLC patterns.
• You will work in the trenches of the legacy codebase, extracting logic and implementing modern, testable solutions using the latest AI-powered development environments.
• Design and implement sophisticated new functionalities within the existing .NET ecosystem, ensuring seamless integration with legacy components.
• Proactively utilize AI coding assistants and advanced environments (e.g., Cursor, Windsurf, Claude Code, or VS Code extensions) to accelerate code comprehension, documentation, and refactoring.
• Act as a high-level escalation point for complex bugs and performance bottlenecks within the legacy environment.
• Utilize Microsoft PowerApps to build rapid, lightweight administrative or maintenance utilities to support the development and operations lifecycle.

Requirements

• 6+ years of professional software development experience, with deep expertise in the .NET/C# stack.
• Proven experience working with older .NET versions (e.g., .NET Framework) and managing the complexities of monolithic architectures.

The Project

Internal Support Tools Evolution You are joining an initiative focused on the evolution, modernization of the Internal Application Landscape. This project involves the strategic transition of well-known cloud services and legacy .NET architectures into a next-generation, AI-augmented, and cloud-native software landscape. Our goal is not simply to "maintain" the existing system, but to proactively transform it—ensuring sovereignty, high-performance scalability, and seamless handover readiness through disciplined engineering. Our Engineering Philosophy We operate at the intersection of Legacy Stability and Modern Innovation.

Our approach is defined by

AI-Augmented Engineering: We utilize advanced AI development environments (such as Cursor, Windsurf, and Claude Code) and cutting-edge model families to accelerate code comprehension, refactoring, and documentation.

Disciplined SDLC Patterns

Every change is backed by structured engineering evidence and rigorous automated testing.

The "Strangler Fig" Modernization

We prioritize risk-mitigated evolution, using sophisticated patterns to wrap, refactor, and eventually replace legacy components.

High-Seniority Autonomy

We operate as a lean, highly autonomous unit. We value "technical detectives" who can navigate ambiguity and perform deep reverse engineering. Mission To drive the technical execution of both high-impact feature development and the deep-dive modernization of our legacy .NET ecosystem. You will be a specialist who finds satisfaction in solving complex puzzles, utilizing AI-assisted tools to accelerate the modernization of our core systems.

Role

Focus This role focuses on high-complexity coding, deep reverse engineering, and AI-augmented productivity.

Deep Reverse Engineering

Analyze and deconstruct complex, undocumented, or "spaghetti" legacy code to understand underlying business rules and technical flows.

Robust Testing & Stability

Write high-quality unit and integration tests to "wrap" legacy modules, providing a safety net for all refactoring efforts.

AI Tooling Proficiency

Hands-on familiarity with AI coding assistants, prompt engineering, or local model experimentation.

Core Skills

Mastery of SOLID principles, design patterns, and advanced debugging/profiling techniques.

Testing Mindset

Strong commitment to TDD and automated testing (Unit/Integration) to protect the legacy core.

Please be informed that our remote working possibility is only available within Hungary due to European taxation regulation.

As Hungary’s most attractive employer in 2025 (according to Randstad’s representative survey), Deutsche Telekom IT Solutions is a subsidiary of the Deutsche Telekom Group. The company provides a wide portfolio of IT and telecommunications services with more than 5300 employees. We have hundreds of large customers, corporations in Germany and in other European countries. DT-ITS recieved the Best in Educational Cooperation award from HIPA in 2019, acknowledged as the the Most Ethical Multinational Company in 2019. The company continuously develops its four sites in Budapest, Debrecen, Pécs and Szeged and is looking for skilled IT professionals to join its team.