Senior .NET Engineer

Coldrun is a Warsaw-based software engineering company building custom software for real-world operations. As a partner to an innovative US-based tech company, we are looking for a Senior Back-end Engineer (.NET) to help develop and scale an ERP-class, multi-tenant SaaS platform that automates production, dispatch, and logistics workflows. You will join a team working on a modular, domain-driven system built with .NET and SQL Server, deployed on Microsoft Azure, and supporting real-time operations across multiple plants, fleets, and business units. Requirements • 6+ years of experience with Microsoft .NET, including at least 4 years with modern .NET (Core / 5+) • 3+ years building production-grade, enterprise-level applications • Strong understanding of RESTful API design, SOLID, DDD, OOP, and common design and architectural patterns • Solid experience with Entity Framework Core (or similar ORM), including migrations and query optimization • Deep knowledge of SQL Server, including schema design, indexing, and execution plan analysis • Experience building scalable, multi-tenant or N-tier SaaS systems • Hands-on experience with Microsoft Azure • Experience securing APIs using JWT and OAuth2 / OpenID Connect, including role-based and permission-based access • Familiarity with Docker, Git, CI/CD pipelines, and Agile workflows • Availability to work US East Coast business hours (-6h) at least 2 days per week • Fluent communication in English and Polish Nice to have • Experience with real-time systems (SignalR or similar) • Exposure to observability tooling (DataDog, Application Insights) • Experience with performance or load testing (JMeter, or similar) • Experience with Azure DevOps • Experience integrating external systems via webhooks or event-driven architectures What we offer • Remote-first setup or hybrid option (Warsaw) • Flexible working hours • Private healthcare • Sports and leisure package • Long-term, stable cooperation • International working environment • Regular team and company events