Backend Developer (Kotlin)

JR United Kingdom; Slough; On-site; GBP 50,000 - 75,000; Full time

Job summary

JR United Kingdom is seeking a Backend Engineer (Kotlin) to enhance their SaaS platform. You will design and implement services, model data in PostgreSQL, and collaborate closely with product and frontend teams. The position offers opportunities to influence architectural decisions and grow within a dynamic and supportive environment.

Benefits

Generous cash compensation and share options

Flexible work hours

Personal development budget

Comprehensive health, vision, and dental plan coverage

33 days paid leave per year

Snacks and drinks provided weekly

Regular team socials and international trips

Qualifications

• Professional experience building Kotlin (or Java) services on Spring Boot.
• Solid knowledge of PostgreSQL schema design and migration tools.
• Comfortable writing tests (JUnit, Testcontainers).

Responsibilities

• Design, implement and maintain Spring Boot services in Kotlin.
• Collaborate daily with the Product Manager and frontend engineers.
• Contribute to and refine CI/CD workflow on GitHub Actions.

Skills

Kotlin

PostgreSQL

Spring Boot

OpenAPI

CI/CD

JUnit

GitHub Actions

Job description

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Synthesized is transforming how the world tests software with AI.

Trusted by global leaders like Deutsche Bank, UBS, and the European Commission, our AI-powered platform enables teams to generate high-quality test data and test cases in seconds—slashing costs, accelerating delivery, and eliminating reliance on production data.

We're a VC-backed company supported by top investors. With strong traction across financial services, healthtech, and telecom, and a $90B+ market in sight, we're scaling fast in 2025 and beyond.

? The Role

We’re looking for a Backend Engineer (Kotlin) to evolve and scale the control-plane of our SaaS platform. With customer adoption climbing, we need extra fire-power to extend core services and keep pace with new feature demand. Reporting to the Backend Team Lead, you’ll build services that power everything the UI depends on. You’ll work closely with Product Management on feature design and pair with frontend engineers. The role offers plenty of scope to shape architecture, own features end-to-end, and putting your stamp on architectural decisions that drive the product forward.

? Key Responsibilities

• Design, implement and maintain Spring Boot services in Kotlin, with a focus on clean architecture and resilience.
• Model data in PostgreSQL, own schema migrations with Liquibase, and access data through jOOQ.
• Treat the OpenAPI contract as the single source of truth. Co-author, review and enforce it across teams, automate server/client generation.
• Practice shift-left testing: write unit and integration tests alongside your code.
• Practice documentation as code: write documentation for new features alongside your code.
• Contribute to and refine our CI/CD workflow on GitHub Actions.
• Collaborate daily with the Product Manager, Team Lead and frontend engineers to de-risk stories, clarify edge cases and deliver iterative value.
• Participate in code reviews and architecture discussions, sharing knowledge and mentoring when opportunities arise.
• Help monitor production with logs/metrics, triaging incidents and feeding learnings back into design and tests.

? About You

• Professional experience building Kotlin (or Java) services on Spring Boot in production.
• Solid knowledge of PostgreSQL schema design, indexing, SQL queries and migration tools (Liquibase or similar) and fluency with jOOQ or similar tools for type-safe data access.
• Comfortable writing tests (JUnit, Testcontainers, MockMVC) and using code-coverage metrics to guide improvements.
• Hands-on with OpenAPI / Protobuf and code-generation workflows; you value strongly typed contracts between services and UI.
• Familiar with GitHub and GitHub Actions (or similar) for CI/CD and environment automation.
• Understanding of cloud-native patterns (containers, REST/gRPC APIs, observability).
• Good grasp of distributed-systems pitfalls, which is relevant to our remote-agent / control-plane topology.
• Practical experience with performance profiling and JVM tuning is a plus.
• Understanding basics of front end development (full stack skills) is a strong plus.
• Clear communicator who enjoys whiteboarding with product and frontend peers and can explain trade-offs to both technical and non-technical stakeholders.
• Continuous learner who values clean code and incremental delivery.
• Wonderful office in the heart of Shoreditch, hybrid 3-days ?
• Generous cash compensation and share options ?
• Flexible work hours
• Personal development budget (coaching, courses, events) ?
• Comprehensive health, vision, and dental plan coverage ️
• 33 days paid leave per year including flexible national holidays ?
• Snacks and drinks provided weekly ?
• Working alongside great people in a friendly and respectful environment ??️
• Company events, regular team socials, and international trips ️

We are committed to an inclusive and diverse workplace at Synthesized. Synthesized is an equal opportunity employer. We do not discriminate based on race, ethnicity, color, ancestry, national origin, religion, sex, sexual orientation, gender identity, age, disability, veteran status, genetic information, marital status or any other legally protected status.