Mid/Senior .NET Developer

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 Job Description Design, develop, and maintain robust Back-end solutions using C# and .NETParticipate in architecture discussions and contribute to technical solution designDevelop and integrate RESTful APIs and SOAP web servicesWork on core modules development and perform refactoring when necessaryCollaborate closely with developers, QA engineers, DevOps specialists, architects, and Product OwnersClarify business and technical requirements with internal and Customer-side teamsWrite and maintain unit, API, and integration testsParticipate in peer code reviews and follow engineering best practicesInvestigate and introduce new technologies and technical improvementsTroubleshoot issues across application, infrastructure, and database layersPrepare and maintain technical documentationContribute to Front-end-related tasks using Angular and TypeScript when needed Qualifications 4+ years of commercial software development experience with C# and .NETStrong experience designing, developing, and integrating Web APIs, including RESTful APIs and SOAP servicesSolid understanding of OOP, SOLID principles, and common design patternsStrong knowledge of Microsoft SQL Server and T-SQLPractical experience with LINQ, ADO.NET, and Entity FrameworkExperience working with event-driven systems and message brokersExperience writing and maintaining unit, API, and integration testsExperience with Angular or another modern Front-end framework/libraryGood knowledge of TypeScriptUnderstanding of Front-end architecture, maintainability, and performance optimizationStrong troubleshooting and debugging skills across application, database, and infrastructure layersConfident Git usage, including branching strategies, pull requests, and code reviewsIntermediate or higher English levelStrong communication skills and ability to work collaboratively in a cross-functional environmentWILL BE A PLUS: Experience with NoSQL databasesExperience using AI-assisted development tools such as GitHub Copilot or Claude