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 55% backend and 45% 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