Fullstack Engineer (Java/Kotlin + React)

What you work on today shapes where you’ll be tomorrow.

Looking for your next challenge as a Fullstack Engineer (Java/Kotlin + React)? We may have the right opportunity for you.

At B3, we start with people and their experience. We match projects to your skills and professional growth path. Our consultants work across a wide range of industries and technologies, delivering IT projects both in Poland and internationally. This allows you to build your career in a deliberate way - not by chance.

We are part of an international organization listed on Nasdaq Stockholm, operating in 11 countries. In Poland, we operate with full autonomy. We choose our technologies, processes, and ways of working while maintaining the highest professional standards.

Join us today.

What we offer

• Work in a Scandinavian culture built on logic, trust, and open dialogue.

• Health and sports benefits tailored to your needs.

• Speed Coaching – short sessions designed to provide new perspectives and solutions.

• Sports training, an internal team, and opportunities to take part in competitions.

Key areas of the role:

• Backend and APIs - Preparing mocks, designing and adjusting APIs in Java/Kotlin within a microservices architecture, enabling integrations with external strategic partners

• Frontend in React - Building responsive web components, checkout funnels and registration paths, and integrating the frontend with the backend and the mobile app

• Building new services the startup way - Working in a greenfield area on services that run outside the core market but are integrated with platform services (payments, login, search), delivering fast with the support of AI and agentic development tools

What you need to join us:

Must have:

• Good programming skills in Java and/or Kotlin and confidence working with microservices

• Hands-on frontend experience: HTML, CSS, JavaScript and modern frameworks (ideally React)

• Clear understanding of REST API principles, working with JSON data and consuming backend endpoints

• Ease of switching between backend and frontend, a problem-solver mindset, flexibility in a not-yet-defined area and exp. with with AI / agentic development tools

• English at B2+ level or higher and Polish

• Right to work in Poland (citizenship, residence card, visa, etc.)

Nice to have:

• Familiarity with CI/CD tools (GitLab CI, Docker)

• Experience with cloud environments

• An eye for modern UX/UI standards, accessibility and Responsive Web Design (RWD)

• Experience integrating with external systems and partners

• Based in or near Warsaw or Poznań (occasional workshops and planning sessions in the office)