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Senior Full-Stack Developer (.Net and React) at JustAnswer. Location Information: Ukraine. About the Role. As a Senior Full-Stack Developer, you will join a mission-critical initiative to build an AI-powered subscription platform for solo professionals (Fount.com). Fount is an independent product unit partially supported by JustAnswer, and you’ll join its core delivery team. We’re developing a category-defining toolset that helps experts get leads, manage communications, and grow their businesses — all enhanced by intelligent AI assistants. . You’ll work across the full stack (.NET Core/C# + React.js), helping build new features like an auction system for lead bidding, expert/customer chats, contracts, and billing tools. Much of the work is greenfield (from the scratch), and you’ll play a key role in defining scalable architecture and shipping impactful features. . What You’ll Do. Design, develop, and maintain full-stack applications, backend logic modules, and front-end experiences using React.js and .NET Core. . Collaborate with Product, UX, and Engineering stakeholders to clarify requirements and contribute to technical planning and documentation. . Conduct code and design reviews, provide architectural input, and mentor junior developers on best practices. . Write and maintain automated unit and integration tests using tools such as Jest, NUnit, or Playwright. . Monitor and support production systems, resolve bugs, run performance audits, and ensure system stability. . Contribute to the implementation of AI-driven features, including prompt-based workflows, RAG pipelines, and personalized assistant flows. . Continuously improve code quality, team velocity, and system reliability through thoughtful technical decisions and rapid iteration. . What We’re Looking For. 5+ years of commercial experience in full-stack software development. . Strong proficiency in .NET Core, C#, and React.js (or deep experience in another modern frontend framework and readiness to learn React). . Experience building and consuming REST APIs, and working with asynchronous backend services. . Familiarity with modern automated testing frameworks (Jest, NUnit, Playwright, etc.). . Comfortable working in a CI/CD environment with agile delivery cycles. . Basic database knowledge and familiarity with performance and scalability considerations. . Proven ability to work independently, own projects end-to-end, and make architectural tradeoffs. . Upper-Intermediate English or higher for effective communication with international stakeholders. . Curiosity and interest in AI-powered applications and emerging technologies. .