Senior Software Engineer, C# / .NET

New Monday

. Design, develop, test and maintain scalable applications in C# and the .NET ecosystem .

Posted 10/15/2026full-timeMannheim • GermanySenior💰 €5,500 - €8,000 per monthWebsite

Core Competencies

Role fit

Core Competencies

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Demonstrates expertise in C# and the .NET ecosystem, with a strong focus on multi-threaded programming, RESTful API design, and automated testing practices. Proven ability to mentor developers and drive improvements in software architecture and performance.

Highest-signal resume keywords

C# 14Multi-Threaded ProgrammingRESTful API DesignAutomated TestingClean Architecture

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills

C#Multi-Threaded ProgrammingRESTful APIOOPSOLID PrinciplesClean CodeTDDUMLHigh-Volume In-Memory Data ProcessingLegacy Modernization

Soft Skills

MentoringCollaborationConstructive FeedbackProblem SolvingCommunication

Tools & Technologies

.NETCI/CDDistributed SystemsMicroservices.NET MAUI

Industry Keywords

Software DevelopmentReal-Time SystemsHardware IntegrationOptical Sensor Data ProcessingDistributed/Service-Oriented Systems

Tech Stack

Tools & technologies

Microservices.NET

About the role

Key responsibilities & impact

Design, develop, test and maintain scalable applications in C# and the .NET ecosystem
Write clean, well-documented code following Clean Architecture and coding standards
Work test-driven and strengthen automated testing practices
Build robust multi-threaded solutions using locking, interlocking and parallelism in .NET
Translate business requirements into technical solutions with product owners, architects and cross-functional teams
Review code and provide constructive feedback
Mentor junior and mid-level developers and provide technical guidance
Drive improvements in architecture, performance, reliability and maintainability
Troubleshoot and resolve complex issues across a distributed software stack
Contribute to CI/CD and modern delivery practices

Requirements

What you’ll need

Deep, hands-on knowledge of C# 14 and modern .NET
Several years of experience with multi-threaded programming
Several years of experience with high-volume in-memory data processing
Solid experience designing and implementing RESTful APIs
Strong command of OOP, SOLID, Clean Code, multi-layer architecture and TDD
Practical experience with automated testing, including unit tests, component tests and mocking
Good working knowledge of UML
Proven experience in hardware-related software development
Degree in Computer Science, Software Engineering, Physics or a related field
Excellent English
Ability to work in international, cross-functional teams
Real-time systems, hardware integration or optical sensor data processing is a strong plus
Experience with legacy modernization, distributed/service-oriented systems or microservices
Knowledge of distributed system design, relational database design or .NET MAUI front-end development is a plus
German language skills are a plus

Benefits

Comp & perks

24 days of annual leave
Hybrid setup with 3 days remote per week
International team
Personal support throughout the hiring process
Opportunity to influence architecture and mentor other developers