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Hi, I'm Oleh Kozii, a full-stack engineer based in Wroclaw, Poland. I specialize in backend development with Node.js (NestJS, Fastify, Express), SQL and NoSQL databases, and building reliable APIs and microservices. I enjoy turning complex requirements into scalable, maintainable solutions and solving tough performance problems. I collaborate closely with frontend, product, and DevOps teams to ship features that users love. In my spare time I explore cloud architectures (AWS, Firebase) and keep up with best practices to improve reliability and developer experience.…Hi, I'm Oleh Kozii, a full-stack engineer based in Wroclaw, Poland. I specialize in backend development with Node.js (NestJS, Fastify, Express), SQL and NoSQL databases, and building reliable APIs and microservices. I enjoy turning complex requirements into scalable, maintainable solutions and solving tough performance problems. I collaborate closely with frontend, product, and DevOps teams to ship features that users love. In my spare time I explore cloud architectures (AWS, Firebase) and keep up with best practices to improve reliability and developer experience.

Oleh Kozii

Full Stack Developer, Back-End Developer, Web Developer, +2

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Hi, I'm Oleh Kozii, a full-stack engineer based in Wroclaw, Poland. I specialize in backend development with Node.js (NestJS, Fastify, Express), SQL and NoSQL databases, and building reliable APIs and microservices. I enjoy turning complex requirements into scalable, maintainable solutions and solving tough performance problems. I collaborate closely with frontend, product, and DevOps teams to ship features that users love. In my spare time I explore cloud architectures (AWS, Firebase) and keep up with best practices to improve reliability and developer experience.…Hi, I'm Oleh Kozii, a full-stack engineer based in Wroclaw, Poland. I specialize in backend development with Node.js (NestJS, Fastify, Express), SQL and NoSQL databases, and building reliable APIs and microservices. I enjoy turning complex requirements into scalable, maintainable solutions and solving tough performance problems. I collaborate closely with frontend, product, and DevOps teams to ship features that users love. In my spare time I explore cloud architectures (AWS, Firebase) and keep up with best practices to improve reliability and developer experience.

Available to hire

Hi, I’m Oleh Kozii, a full-stack engineer based in Wroclaw, Poland. I specialize in backend development with Node.js (NestJS, Fastify, Express), SQL and NoSQL databases, and building reliable APIs and microservices. I enjoy turning complex requirements into scalable, maintainable solutions and solving tough performance problems.

I collaborate closely with frontend, product, and DevOps teams to ship features that users love. In my spare time I explore cloud architectures (AWS, Firebase) and keep up with best practices to improve reliability and developer experience.

Skills

Experience Level

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Intermediate

Intermediate

Intermediate

Language

Ukrainian

Fluent

English

Advanced

Polish

Beginner

Work Experience

Backend Engineer at Appexoft

January 1, 2023 - October 21, 2025

Designed and implemented new features for existing products to enhance functionality and user experience. Improved application performance by profiling and optimizing inefficient code paths. Modernized and refactored legacy codebases to increase maintainability, readability, and stability.

Full Stack Engineer at Kevych Solutions

January 1, 2023 - Present

Led and managed the end-to-end software development lifecycle for multiple client projects. Designed and made key decisions on system architecture, ensuring scalability and maintainability. Coordinated cross-functional teams to ensure timely and high-quality delivery. Maintained and optimized product infrastructure to improve reliability and performance. Enhanced existing features, reducing load times by 30–40%. Prepared accurate product estimates and delivery timelines. Refactored legacy codebases to improve maintainability and performance.