Sii ensures that all employment-related decisions are made solely on the basis of qualifications and competencies. We are committed to equal treatment of all individuals, regardless of any protected characteristics, and promoting a diverse and inclusive work environment.We are looking for a .NET Developer to join the front-office Trading Tool team that builds and maintains high-performance applications used by traders for market-making. You will work on a complex system combining WPF/DevExpress interfaces, browser-based tools, and integrations with multiple internal APIs. The team operates in a distributed setup between France and Poland.The role requires working from the Warsaw office two to three days per week.Your tasks Design, develop, test, and deploy high-performance trading applications operating in a multi-threaded environment Build and maintain WPF/DevExpress user interface components used by traders Translate technical and functional requirements into detailed user stories and collaborate closely with Agile Masters and Business Analysts Deliver and support applications through Continuous Delivery (DevOps) Maintain and improve production support tools and participate in non-regression testing Recommend and implement improvements to application performance, architecture, and development processes Provide clear and consistent progress updates to traders and stakeholders Requirements Minimum 5 years of experience in backend C# development Strong understanding of multithreaded programming and microservices architecture Experience with WPF/DevExpress Fluency in English (spoken and written) Excellent communication and teamwork skills Proactive, solution-oriented, and collaborative mindset Open to a hybrid work model (2-3 days per week on-site) Fluent in Polish required Residing in Poland required What we offer  Great Place to Work since 2015 - it’s thanks to feedback from our workers that we get this special title and constantly implement new ideas  Employment stability - revenue of PLN 2.1BN, no debts, since 2006 on the market  We share the profit with Workers - over PLN 76M has already been allocated for this aim since 2022  Attractive benefits package - private healthcare, benefits cafeteria platform, car discounts and more  Comfortable workplace – class A offices or remote work  Dozens of fascinating projects for prestigious brands from all over the world  PLN 1 000 000 per year for your ideas - with this amount, we support the passions and voluntary actions of our workers  Investment in your growth – meetups, webinars, training platform and technology blog – you choose  Fantastic atmosphere created by all Sii Power People  Join the Sii team – develop your skills, gain experience, and build your career!