We are looking for FullStack Engineer (.NET & React)Location: Kraków / Hybrid (7 days in the office per month)Contract Type: B2B ContractSeniority: Mid / Senior  About the ProjectJoin a high-impact modernization initiative for a leading player in the banking sector. We are transforming a portfolio of approximately a dozen .NET applications and MSSQL databases into a modular, cloud-native Azure architecture.As a FullStack Engineer, you will play a dual role: evolving existing production services (including legacy UI and desktop components) while systematically extracting business logic to re-implement it into a modern, scalable ecosystem. This is a unique opportunity to influence the transition from monolithic architectures to high-performance, distributed cloud services. Your Responsibilities Design & Development: Build backend services and APIs using .NET 6/8 following Clean Architecture and DDD patterns. Frontend Evolution: Develop and maintain React + TypeScript frontends, managing the incremental migration from legacy UI modules. Modernization: Read, refactor, and extract complex business logic from legacy .NET codebases and T-SQL stored procedures. Quality Assurance: Write and maintain comprehensive automated tests (Unit, Integration, Contract, and E2E). DevOps & Observability: Create CI/CD pipelines (Azure DevOps/GitHub Actions) and instrument services for deep observability (metrics, logs, distributed traces). Collaboration: Participate in domain modeling, architecture discussions, and Agile ceremonies with Architects and Product Owners.  Skills & Experience We Require Experience: 5+ years of commercial experience with C# and the .NET ecosystem (both Framework and .NET Core/6+). Database Expertise: Strong proficiency in EF Core and MSSQL (including query tuning, transactions, and indexing). Frontend: Solid production experience with React and TypeScript. Web Services: Practical experience in building and securing REST APIs (Auth, Versioning, Validation). Cloud: Familiarity with Azure services (App Service, Functions, SQL, Service Bus, Storage). Testing & Tooling: Experience with xUnit, Jest, and Playwright/Cypress, as well as disciplined Git practices. Legacy Handling: The ability to read and reason about legacy codebases (ASP.NET MVC, Razor, WPF, or WinForms). Communication: English at a B2+ level for technical documentation and team collaboration.  Nice to Have Experience with Infrastructure as Code (Terraform or Bicep). Knowledge of Docker and Kubernetes (AKS). Background in migrating monoliths to microservices. Azure Developer Associate certification.  What We Offer Impact: Real influence on the architecture and the cloud migration roadmap. Autonomy: Direct collaboration with Tech Leads and Architects in a flat structure. Modern Stack: Opportunity to work with the latest .NET versions (6/8) and React. Efficiency: Fast technical onboarding with immediate access to repos, CI/CD pipelines, and monitoring tools. Flexible Hybrid Model: Remote-first approach with only 7 planned days in the Kraków office per month. Benefits : Luxmed and Multisport Card