Principal / Senior Full Stack Engineer

Svitla Systems Inc. is looking for a Principal / Senior Full Stack Engineer with Java and  React for a full-time position (40 hours per week) in Poland. Our client is a digital marketing company that offers email marketing, social media marketing, event marketing, and online survey tools to assist organizations in expanding their businesses by fostering stronger customer relationships.  Overlap till 20:00 CET. REQUIREMENTS 8+ years of experience in developing large-scale applications. Proven experience as a Java Back End Developer with successful project implementations. Strong understanding of Java programming and server-side frameworks (e.g., Spring, Spring Boot). Experience in frontend development with HTML, CSS, and JavaScript (React preferred) to create and maintain essential UI components and support end-to-end functionality. Solid experience with AI coding tools like Clause, Cursor, GenAI (LLMs, RAGs, AI agents) is a huge plus. In-depth understanding of the software development life cycle (SDLC) and agile methodologies. Knowledge of AWS cloud, specifically with Lambdas. Experience in integration of the 3-rd party APIs. Experience in working with legacy codebases and refactoring. Expertise in designing, developing, testing, and maintaining scalable backend applications. Knowledge of build tools (e.g., Maven, Gradle) and CI/CD pipelines (e.g., Jenkins, GitLab CI). Experience with unit testing (e.g., JUnit) and integration testing. Familiarity with database design, optimization, and query tuning for both relational (e.g., MySQL, PostgreSQL) and non-relational databases (e.g., MongoDB). Expertise in designing and implementing RESTful APIs and API standards (e.g., OpenAPI). Understanding of microservices architecture. Knowledge of containerization and orchestration tools (e.g., Docker, Kubernetes). Familiarity with version control systems (e.g., Git). Familiarity with test-driven development (TDD) practices. Experience with SaaS Solutions development is a huge plus. Knowledge of design patterns, best practices in Java development, and secure coding practices. RESPONSIBILITIES Participate actively in product design, development, and code reviews, primarily focusing on backend features with some front-end work. Contribute towards strategic initiatives and integrations with third-party billing and payment systems. Review team PRs and improve observability and overall quality of code. Investigate and resolve issues within the billing ecosystem. Engage in retrospectives to continually improve processes. Collaborate with PMs and senior developers to understand business needs and identify the best technical solutions. Mentor junior team members on best practices, architecture, and development.