Senior Full-Stack Engineer (NestJS and React)

N-iX is looking for a Senior Full-Stack Engineer to join a team modernizing a large ERP/PSA platform for a US-based software company. This role combines hands-on development with technical decision-making, with approximately 65% backend and 35% frontend work. You will build new features, explore complex business logic, and help shape the platform’s evolution using TypeScript, NestJS, React, and Azure. Responsibilities: - Design and implement end-to-end features using NestJS and React. - Analyze the existing codebase, understand business workflows, and contribute to the gradual modernization of the platform. - Design and optimize relational database schemas and queries. - Participate in system design, architecture discussions, and technical decision-making. - Work directly with technical and business stakeholders to clarify requirements and translate business needs into solutions. - Ensure solutions meet security, performance, scalability, and maintainability requirements. - Contribute to code reviews, automated testing, and CI/CD improvements. - Identify technical risks, manage dependencies, and proactively communicate delivery concerns. - Contribute to backlog refinement, planning, and Agile ceremonies. Requirements: - 5+ years of commercial software engineering experience, including backend and frontend development with TypeScript. - Hands-on experience with NestJS and React. - Practical experience building and integrating REST APIs and GraphQL. - Experience developing complex backend systems with substantial business logic. - Solid understanding of distributed systems and microservices-based architectures. - Strong expertise in relational databases such as MySQL or PostgreSQL, including schema design, query optimization, and performance analysis. - Hands-on experience with Apache Kafka. - Hands-on experience with Microsoft Azure. - Experience analyzing large legacy codebases and working with limited documentation. - Experience contributing to system design and technical decisions. - Strong analytical, problem-solving, and stakeholder communication skills. - Experience working in Agile, Scrum, or Kanban teams. - Upper-Intermediate or higher English and proficiency in Ukrainian for daily team communication. Nice to have: - Experience with ERP platforms, financial systems, enterprise SaaS, multi-tenant applications, or large B2B portals. - Experience with stored procedures, database functions, and complex SQL. - Knowledge of PHP and Microsoft SQL Server, particularly stored procedures. - Experience reverse engineering existing systems and incrementally modernizing legacy applications. - Experience with AI-assisted development tools such as GitHub Copilot, Claude, or Cursor. We offer*: - Flexible working format - remote, office-based or flexible - A competitive salary and good compensation package - Personalized career growth - Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more) - Active tech communities with regular knowledge sharing - Education reimbursement - Memorable anniversary presents - Corporate events and team buildings - Other location-specific benefits *not applicable for freelancers