Senior Fullstack Engineer (Kotlin&React)

Role overview

A senior full-stack engineer is needed to take a technical lead on API and integration architecture for a team building modern web applications and backend services. The role blends hands-on coding with architectural decision-making, defining standards, and guiding engineering discussions.

Responsibilities

- Design and develop APIs that enable integrations with external business partners - Take a technical lead on integration architecture and contribute to key architectural decisions - Define API contracts following an API-first approach using OpenAPI or Swagger - Develop backend services with Java and Kotlin - Build modern web applications with React and TypeScript - Define and promote software development standards and best practices - Prepare and maintain technical documentation - Lead technical discussions and support the team in making sound engineering decisions - Work with distributed systems and complex system-to-system integrations - Participate in an on-call rotation

Requirements

- Strong commercial experience with Java and Kotlin - Proven experience designing, building, and maintaining REST APIs - Hands-on experience with API-first design and OpenAPI or Swagger - Solid knowledge of React and TypeScript - Good understanding of distributed systems and integrations between them - Practical knowledge of OAuth 2.0 and OpenID Connect - Practical experience using AI-powered assistants such as Claude Code, GitHub Copilot, or Cursor - Experience making architectural decisions and leading technical discussions - Strong communication and collaboration skills - English at minimum B2 and Polish at minimum B1 - Willingness to visit a Warsaw office one to two times per quarter

Nice to have

- Experience with data security and regulatory compliance, particularly GDPR - Experience with B2B integrations and external partner work - Applied GenAI within the SDLC or interest in agent-based workflows

Benefits and work setup

Remote work within the European Union; a valid EU work permit is required, with occasional Warsaw office visits.