Kotlin Developer (f/m/x)

Sii Poland; Warszawa; On-site; PLN 180,000 - 240,000; Full time

Benefits offered by this job

Great Place to Work

Solid financial situation

Contracts with the biggest brands

Centre of internal trainings

Many experts you can learn from

Open and accessible management team

Profit sharing

Passion Sponsorship program

Regular integration events and trips

Comfortable and well-equipped offices

MySii app

Medical care

Job summary

Sii Poland is seeking an experienced backend engineer to join a fintech platform developing expense management and integration with banks, accounting, and HR systems. You will design, build, and maintain scalable microservices in Kotlin, with a focus on performance and reliability.

You'll mentor teammates, participate in code reviews and migrations, and work with AWS, Kubernetes, PostgreSQL, and observability tools to continuously improve architecture.

Qualifications

• 5+ years of professional software development experience.
• Strong Kotlin server-side expertise.
• Experience with distributed systems, microservices and cloud environments.
• Proficiency with PostgreSQL and testing tools (JUnit, Testcontainers).
• Familiarity with observability tools such as Grafana.
• Excellent problem-solving and mentorship mindset.
• English at least B2.
• Residing in Poland.

Responsibilities

• Lead design, build, and maintenance of scalable microservices primarily using Kotlin.
• Collaborate with cross-functional teams across Platform, Services, SMB, and other domains.
• Analyze system performance and implement optimizations for high reliability and scalability.
• Participate in code reviews, post-mortems, and mentor other engineers.
• Proactively improve architecture and quality, guiding migrations and technical challenges.

Skills

Leadership

Mentoring

Collaboration

Problem-solving

English proficiency

Tools

Kotlin

PostgreSQL

JUnit

Testcontainers

Grafana

AWS

Kubernetes

Job description

Join a team working on a modern fintech platform that supports company expense management. The project focuses on developing a finance solution that enables seamless integration of financial tools (including payment cards, expense management, and invoice handling) directly into partner systems such as banks, accounting platforms, and HR solutions. The product being developed allows companies to simplify financial processes, automate settlements, and gain full real-time control over their spending.

Your tasks

• Leading initiatives to design, build, and maintain scalable microservices primarily using Kotlin
• Collaborating with cross-functional teams to develop innovative solutions across Platform, Services, SMB, and other domains
• Analyzing system performance and implementing optimizations to ensure high reliability and scalability
• Participating in code reviews, post-mortems, and providing mentorship to other engineers
• Proactively improving the architecture and quality of solutions, and leading the team through technical challenges and migrations

Requirements

• Minimum 5 years of professional experience in software development
• Expertise in server-side languages, especially Kotlin, and experience with distributed systems, microservices, and cloud environments (e.g., AWS, Kubernetes)
• Proficiency with relational databases like PostgreSQL, testing frameworks (e.g., JUnit, Testcontainers), and observability tools like Grafana
• Strong problem-solving skills and a collaborative mindset to mentor and upskill your teammates
• Very good knowledge of English - min. B2 level
• Residing in Poland required

Nice to have

• Previous work in the fintech industry or with financial products
• Knowledge of topics related to payments, cards, or accounting
• Experience working in a scale-up environment
• Proficiency in one of the following front-end technologies: React or TypeScript

Job no. JOB-EQKGG

Sii ensures that all hiring decisions are made solely on the basis of qualifications and competence. We are committed to equal and fair treatment of all, regardless of legally protected characteristics. At Sii, we promote a diverse and inclusive work environment, in full compliance with applicable anti-discrimination laws.

Benefits For You

• Great Place to Work
• Solid financial situation
• Contracts with the biggest brands
• Centre of internal trainings
• Many experts you can learn from
• Open and accessible management team
• Profit sharing
• Passion Sponsorship program
• Regular integration events and trips
• Comfortable and well-equipped offices
• MySii app
• Medical care