Віталій

Vitalii Koltok
Back-End Developer

[open contact info](look above in the "contact info" section) | [open contact info](look above in the "contact info" section) | Warsaw, Poland | Remote

PROFILE
Product-oriented Backend Java Developer with 3+ years of experience building mission-critical systems for healthcare and
education sectors serving 2M+ users. Proven track record of designing scalable, reliable backend services that deliver
measurable business impact - including supporting legacy-to-modern migrations that enabled 18% revenue growth and
optimizing core workflows to reduce task completion time by 30%. Combines strong product thinking with deep technical
expertise in Java, Spring Boot, SQL, and distributed-service patterns, specializing in complex system integrations, data
consistency, and zero-downtime deployments. Bridges business needs and technical execution by translating stakeholder
requirements into secure, maintainable APIs and backend architectures that perform under high-stakes, real-world workloads.

PROFESSIONAL EXPERIENCE

Back-End Developer Eurosoft, Warsaw, 01.2023 - Now

Architected and developed the backend service for the web modernization of “EuroSoft Przychodnia” for Poland’s top-2
healthcare software provider, supporting 2,000+ healthcare facilities, 800+ hospitals, and 10,000+ medical professionals
nationwide.

● Implemented a scalable API layer (REST) and service architecture that enabled the new web platform to operate
reliably under nationwide clinical workloads, improving overall system responsiveness and stability, that directly
increased company revenue by 18%.
● Engineered a robust data access and compatibility layer over a legacy SQL database with over 5M patient records and
26 years of history, including schema reverse - engineering, safe query optimization, and backward - compatible
contracts - ensuring zero data loss and zero downtime while the desktop and web systems ran in parallel.
● Partnered with physicians and operational staff to translate clinical workflows into backend business logic, reducing
edge-case errors and cutting end-to-end task completion time by 30%.
● Built migration-safe deployment patterns that supported gradual rollout of new modules without interrupting
day-to-day hospital operations.
● Implemented security and compliance - focused controls appropriate for healthcare systems, strengthening data
integrity and traceability across clinical workflows.

KEY SKILLS
Soft skills: Time Management, Problem solving, Collaboration, Creativity, Critical Thinking, Emotional Intelligence,
Flexibility

Technical skills: Java 17, Spring Boot, Hibernate, JUnit5, Postman, PostgreSQL, PL-SQL, T-SQL, Maven, GIT & Version
Control, Docker, SOLID

EDUCATION
Bachelor of Computer Science - Polish-Japanese Academy of IT in Warsaw

LANGUAGES

UKRAINIAN – NATIVE , ENGLISH – C1, POLISH – C1