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