Middle/Senior .NET Developer (Construction)

Sigma Software; Kraków, Warszawa; On-site; PLN 180,000 - 300,000; Full time

Job summary

Sigma Software in Kraków is seeking a Middle/Senior .NET Developer to contribute to architecture discussions, product evolution, and backend solutions for the European construction sector. You will join a mature delivery team, collaborating with architects, QA, DevOps, and Product Owners.

The role focuses on building robust C#/.NET backends, REST/SOAP services, and data layer with SQL Server, EF, and Kafka, with opportunities to influence frontend tasks using Angular/TypeScript as needed.

Qualifications

• 4+ years of commercial software development with C# and .NET
• Strong experience designing, developing, and integrating Web APIs, including RESTful APIs and SOAP services
• Solid understanding of OOP, SOLID principles, and common design patterns
• Strong knowledge of Microsoft SQL Server and T-SQL
• Practical experience with LINQ, ADO.NET, and Entity Framework
• Experience with event-driven systems and message brokers
• Experience writing and maintaining unit, API, and integration tests
• Experience with Angular or another modern Front-end framework/library
• Good knowledge of TypeScript
• Understanding of Front-end architecture, maintainability, and performance optimization
• Strong troubleshooting and debugging skills across application, database, and infrastructure layers
• Confident Git usage, including branching strategies, pull requests, and code reviews
• Intermediate or higher English level
• Strong communication skills and ability to work collaboratively in a cross-functional environment

Responsibilities

• Design, develop, and maintain robust Back-end solutions using C# and .NET
• Participate in architecture discussions and contribute to technical solution design
• Develop and integrate RESTful APIs and SOAP web services
• Work on core modules development and perform refactoring when necessary
• Collaborate closely with developers, QA engineers, DevOps specialists, architects, and Product Owners
• Clarify business and technical requirements with internal and Customer-side teams
• Write and maintain unit, API, and integration tests
• Participate in peer code reviews and follow engineering best practices
• Investigate and introduce new technologies and technical improvements
• Troubleshoot issues across application, infrastructure, and database layers
• Prepare and maintain technical documentation
• Contribute to Front-end-related tasks using Angular and TypeScript when needed

Skills

C#/.NET

REST APIs

SOAP services

Angular

TypeScript

SQL Server

Entity Framework

Kafka

Azure

Git

English communication

Tools

NoSQL databases

Job description

Middle/Senior .NET Developer (Construction)

• Full-time

Join a product-focused engineering team developing solutions for the European construction industry. We are looking for a Middle/Senior .NET Developer who is ready to contribute not only to implementation but also to architecture discussions, technical improvements, and product evolution.

At Sigma Software, you will become part of a mature delivery team with predominantly Senior-level specialists, collaborating closely with architects, QA engineers, DevOps experts, and Product Owners.

CUSTOMER

Our Customer is a European technology company specializing in solutions for construction site security, access management, and operational transparency. Over the past 15+ years, the company has evolved from a smart-lock product into a large ecosystem of web, mobile, and server-side solutions supporting construction businesses across Europe. The engineering organization includes distributed international teams and long-term collaboration with Sigma Software specialists.

PROJECT

The project is part of a large-scale product ecosystem designed for the European construction market. The platform helps construction companies manage access control, subcontractor relationships, security compliance, and operational risks across construction sites.

In this role, you will contribute to a system focused on analyzing companies involved in the construction process. The product enables site operators to monitor subcontractors, maintain compliance standards, and reduce long-term reputational and operational risks.

Project technologies: C#, .NET, REST APIs, SOAP, MS SQL Server, Entity Framework, Kafka, Angular, TypeScript, Azure

• Design, develop, and maintain robust Back-end solutions using C# and .NET
• Participate in architecture discussions and contribute to technical solution design
• Develop and integrate RESTful APIs and SOAP web services
• Work on core modules development and perform refactoring when necessary
• Collaborate closely with developers, QA engineers, DevOps specialists, architects, and Product Owners
• Clarify business and technical requirements with internal and Customer-side teams
• Write and maintain unit, API, and integration tests
• Participate in peer code reviews and follow engineering best practices
• Investigate and introduce new technologies and technical improvements
• Troubleshoot issues across application, infrastructure, and database layers
• Prepare and maintain technical documentation
• Contribute to Front-end-related tasks using Angular and TypeScript when needed

• 4+ years of commercial software development experience with C# and .NET
• Strong experience designing, developing, and integrating Web APIs, including RESTful APIs and SOAP services
• Solid understanding of OOP, SOLID principles, and common design patterns
• Strong knowledge of Microsoft SQL Server and T-SQL
• Practical experience with LINQ, ADO.NET, and Entity Framework
• Experience working with event-driven systems and message brokers
• Experience writing and maintaining unit, API, and integration tests
• Experience with Angular or another modern Front-end framework/library
• Good knowledge of TypeScript
• Understanding of Front-end architecture, maintainability, and performance optimization
• Strong troubleshooting and debugging skills across application, database, and infrastructure layers
• Confident Git usage, including branching strategies, pull requests, and code reviews
• Intermediate or higher English level
• Strong communication skills and ability to work collaboratively in a cross-functional environment

WILL BE A PLUS:

• Experience with NoSQL databases
• Experience using AI-assisted development tools such as GitHub Copilot or Claude