Backend Developer (Kotlin / Spring Boot / PostgreSQL)

We are looking for a strong Backend Developer to join our SaaS platform development.
 

Long-term cooperation preferred. Full-time role.

This is not a generic Java backend role. Our project is built around Kotlin, and we need someone with real commercial experience working on production backend systems.
 

Project context:
We already have an existing backend, an active development process, and a growing product with multiple modules. The team already includes 2 backend developers, 1 frontend developer, a PM, and a QA engineer. We need another backend developer who can work inside an established codebase, understand business logic, collaborate effectively with the team, and deliver reliable backend features without breaking existing flows.
 

Core stack:
- Kotlin
- Spring Boot 3.x
- JDK 21
- Spring Data JPA / Hibernate
- PostgreSQL
- Flyway
 

Important experience:
- Spring Security + JWT
- REST API design and implementation
- Docker
- Swagger / OpenAPI
- Quartz Scheduler or similar scheduled job systems
- AWS S3 or similar file storage integrations
- transactional safety and race condition awareness

Nice to have:
- AOP
- pgvector / vector search
- Spring AI / OpenAI integrations
- SendGrid or similar email services
- SMS providers such as Sinch or Twilio
- Web Push / VAPID
- multi-tenant SaaS experience
- gamification / wallet / points / leaderboard logic
 

What you will work on:
- building new backend modules and endpoints
- extending existing REST APIs
- implementing business logic in an existing production codebase
- working with RBAC and permission systems
- supporting multi-tenant company-based architecture
- improving transactional consistency in sensitive flows
- integrating external services such as storage, notifications, and AI-related features
 

What matters to us:
- real hands-on Kotlin backend experience
- ability to read and extend existing code, not only build from scratch
- careful engineering mindset
- understanding of edge cases, security, permissions, and data isolation
- ability to use modern AI-assisted engineering tools effectively as part of a fast and reliable development workflow
- clear communication

Language requirements:
- Russian or Ukrainian — required
- English — not mandatory, but a basic working level is a plus

Modern workflow:
We strongly prefer developers who are comfortable using modern AI-assisted engineering tools such as ChatGPT, Claude, Cursor, GitHub Copilot, Antigravity, or similar tools in their daily workflow. We value people who can use AI to move faster, while still thinking independently, reviewing generated code critically, and maintaining production-level quality.
 

Please do not apply if:
- your background is mainly Java and Kotlin is only minor
- you mostly worked on simple CRUD apps
- you are not comfortable with existing production codebases
- you do not actively use modern AI-assisted development tools in your workflow
- you need step-by-step supervision for every task
 

To apply, please include:
1. Short summary of your Kotlin + Spring Boot backend experience
2. 2–3 relevant projects
3. Your experience with Spring Security / JWT, PostgreSQL, Flyway, Docker, and scheduled jobs
4. Whether you worked with multi-tenant SaaS systems and RBAC
5. Whether you used AI coding tools in real development workflow
6. Your availability per week
7. GitHub profile or GitHub link

Also answer these questions:
1. What is the biggest backend project you personally built with Kotlin?
2. How would you prevent cross-company data leakage in a multi-tenant SaaS system?
3. What AI coding tools do you actively use, and how do they help you in real backend work?