We’re seeking a Senior Full Stack .NET Developer to join our team and help build scalable, high-performance web applications and APIs that empower thousands of product sellers worldwide. You’ll work across the full stack, from backend services to frontend interfaces, ensuring reliability, quality, and long-term scalability in a fast-evolving SaaS environment.About the ProjectYou’ll join a global software team developing a market-leading inventory management platform that supports merchants in selling, tracking, and optimizing products across multiple online and offline channels. The platform processes millions of orders per year and integrates with a wide ecosystem of e-commerce, retail, and logistics partners to simplify complex supply chain operations. This role requires a small overlap with U.S. working hours for collaboration with the client’s team.Key Responsibilities: Design, build, and maintain web applications and RESTful APIs using C#, .NET Framework, JavaScript, and SQL Server; Collaborate closely with product managers, QA engineers, and developers to translate business needs into reliable, scalable solutions; Write clean, testable, and maintainable code aligned with modern development practices; Implement efficient data access using Entity Framework and optimize queries, stored procedures, and data models; Troubleshoot and resolve application issues, including performance bottlenecks and system bugs; Participate in code reviews, mentor peers, and contribute to a culture of continuous improvement; Work in an agile environment, proactively driving the quality and evolution of business-critical systems. Qualifications: 6+ years of experience in full-stack development using .NET technologies, SQL Server, and JavaScript; Proven expertise with C# and .NET Framework for building modern web applications and services; Strong proficiency in Microsoft SQL Server and understanding of query optimization and database design; Experience with Entity Framework for data access and ORM; Familiarity with Git or similar version control systems and agile methodologies; Strong problem-solving mindset and a commitment to clean, maintainable architecture. In exchange for your skills, we offer: Supportive relationships, built on transparency and a flat structure, in a diverse and multinational team; Office in the center of historical Kraków, where your dog is always welcome; Flexibility when it comes to working from the office or home; Perks include Multikafeteria, Group Life Generali insurance, Signal Iduna, Multisport, language lessons 1:1; Sport and other events, including weekly running, squash, and team lunches on the house; Free tea, coffee, and all-you-can-eat fruits and nuts in the office. The recruitment process includes: HR screening 30min zoom call; 1h technical interview; General call with the team leader; Making an offer meeting.