Senior Fullstack Developer .NET + React

We are looking for a Fullstack .NET Developer to work on the development of business applications in an Agile environment. The role combines backend development in C#/.NET, frontend implementation in React 18+, and analysis/improvement of existing code, including legacy components.This position is a good fit for someone who enjoys working closely with a delivery team, cares about code quality, and can contribute not only to implementation but also to solution design.Key responsibilitiesDevelop software in C#/.NET based on technical and functional documentation.Implement frontend features in React.Analyse, maintain, and extend existing code, including legacy code.Contribute to solution architecture and technical design.Debug, profile, and analyse application performance.Collaborate closely with the delivery team: Testers, Analysts, and Product Owner.Work in Agile methodologies, especially Scrum.Ensure code quality, maintainability, and alignment with development best practices.RequirementsMinimum 5 years of experience developing applications in .NET.Minimum 3 years of experience developing applications in React.Very good knowledge of C# and the .NET ecosystem:.NET Framework,.NET Standard,.NET Core,.NET.Experience with React 18+.Strong debugging, profiling, and performance analysis skills.Knowledge of DDD, Clean Code, and SOLID principles.Understanding of architectural patterns and asynchronous communication.Good knowledge of T-SQL and SQL Server Management Studio.Experience working with Visual Studio.English at B2 level or higher.Fluent Polish.Nice to haveExperience building views for mobile applications.Experience developing applications for the financial sector.Test automation experience, e.g. Postman, Playwright.Knowledge of WCAG accessibility standards.