Senior Backend Developer (Kotlin/Spring Boot) - Full Remote Europe

ABOUT THE OPPORTUNITY

A technically ambitious project in the healthtech sector is looking for a Senior Backend Developer to help build a custom FHIR server from the ground up. This is a genuinely complex, abstraction-heavy engineering challenge: you won't be building CRUD endpoints — you'll be implementing a dynamic query engine that operates on flexible parameters and FHIR structure definitions at runtime. If you thrive on high-abstraction backend work and want to contribute to healthcare infrastructure that matters, this is a strong opportunity.

Language: English B2 minimum | Level: Senior | Location: Fully remote (Europe-based, ideally Portugal)

PROJECT & CONTEXT

A Dutch healthtech company is replacing its commercial FHIR server with a custom-built implementation to overcome long-term scalability and migration constraints. The foundations are already in place — basic server framework, validation logic, conversion framework, and initial queries — and you'll be joining to implement the remaining components, with a focus on the query engine. You'll work closely with a team of 3 internal developers, aligning on design decisions, task division, and progress. Design and architecture are driven collaboratively with the internal team — this is not a solo engagement.

Stack: Kotlin, Spring Boot, PostgreSQL (JSONB), Exposed (ORM), HAPI FHIR, FHIR R4, JUnit, OAuth/Zitadel, SpiceDB (planned)

WHAT WE'RE LOOKING FOR

• Demonstrable experience building abstract backend implementations — query engines, rule engines, dynamic data processing systems, or comparable high-abstraction work
• Strong ability to work at a high level of abstraction — the query engine operates on dynamic parameters and FHIR structure definitions, not a fixed set of operations
• Solid experience with Kotlin and/or JVM-based backend development; Spring Boot experience strongly preferred
• Experience with PostgreSQL, including JSONB storage patterns and complex relational query design
• Ability to implement and maintain a comprehensive JUnit test suite alongside production code
• Strong communication and collaboration skills — you'll be working closely with the internal team on a shared task breakdown, not independently
• Comfortable aligning on design decisions, surfacing blockers, and adapting approach based on team feedback
• English B2 or above — required for daily collaboration with an international team
• Based in Europe (Portugal preferred), available to work fully remote

NICE TO HAVE

• Familiarity with the HL7 FHIR standard (R4) — including resource structures, REST APIs, and search/query capabilities
• Experience with HAPI FHIR library
• Background in or affinity with the healthcare sector
• Exposure to SpiceDB or similar authorisation frameworks
• Experience with OAuth flows and identity providers such as Zitadel