FullStack .NET Developer (React)

About Optiveum and our ClientOptiveum is a boutique talent advisory firm. We help our clients build high-performance technology teams that move the needle. We are currently looking for a Senior FullStack .NET Developer for our client—a fast-growing US-based leader in the Financial Technology sector. With a major engineering hub in Warsaw, they are blending American innovation and "move-fast" culture with top-tier Polish engineering talent. You’ll be joining an environment that skips the bureaucracy in favor of high ownership, architectural excellence, and a product-first mindset. The RoleAs a Senior FullStack Engineer, you aren’t just executing tickets; you are a product builder. You will bridge the gap between robust, high-scale backend services and modern, highly interactive user interfaces. This role is perfect for someone who thrives in a fast-paced US tech culture, enjoys solving complex distributed systems puzzles, and cares deeply about delivering a world-class User Experience (UX). Your ResponsibilitiesFull-Scale Development: Own features end-to-end, from database schema and API design to the final React component. Architecture & Scale: Contribute to the evolution of a Cloud-Native microservices architecture on Azure, designed to handle global traffic. Engineering Excellence: Maintain high standards (SOLID, Clean Code, Design Patterns) while maintaining the velocity needed for a competitive US market. Frontend Leadership: Drive the development of responsive, high-performance web applications using React. Global Collaboration: Partner closely with US-based Product Managers and Stakeholders to translate vision into scalable technical reality. Mentorship: Lead by example through Code Reviews and knowledge sharing, helping elevate the Warsaw engineering hub. RequirementsBackend Expertise: 5+ years of experience in .NET (.NET 6/8+) and C#. Expertise in building RESTful APIs and event-driven architectures. Frontend Mastery: Solid experience with React and TypeScript. Familiarity with state management (Redux, Zustand, or React Query). Cloud-Native Mindset: Practical experience with Azure (App Services, Functions, Service Bus, Cosmos DB/SQL). Database Knowledge: Strong skills in SQL Server and Entity Framework Core. Modern DevOps: Hands-on experience with Docker, Kubernetes, and CI/CD pipelines (Azure DevOps/GitHub Actions). Language: Excellent English (C1) – essential for daily collaboration with the US team. Nice to HaveExperience in high-growth FinTech, WealthTech, or high-frequency trading environments. Knowledge of testing frameworks (xUnit, Jest/Cypress). Familiarity with Web Performance optimization and Accessibility (WCAG). What We OfferUS Tech Culture: A transparent, high-growth environment that values "radical candor," innovation, and taking initiative. Professional Growth: Access to the latest tech—we operate on the "bleeding edge" of .NET and React. Modern Warsaw Office: A vibrant, well-located hub for collaboration, combined with a flexible hybrid/remote policy. Competitive Compensation: 18.000 - 25000 PLN B2B Global Scale: Your code will power mission-critical systems used by financial professionals and institutions across the US and globally.