Backend Mid-level Developer (Java/Kotlin)

We are Red Black Tree, a Serbian software company with over 10 years of experience working for clients from EU and USA.

With a passion for technology and a commitment to excellence, we specialize in developing complete software solutions tailored to meet the needs of businesses across diverse industries, from architecture and development to testing and maintenance.

In our approach to work, we nurture professionalism, quality, respect for deadlines and constant striving for personal progress, always maintaining the passion and enthusiasm that brought us here.

Today, boasting a workforce of approximately 70 dedicated professionals, we have expanded our presence with offices in Belgrade and Čačak, and we are still growing.

We actively seek hard-working, dedicated, dynamic individuals who are not afraid to take risks, learn from others, and embrace new challenges.

What we provide

  • Hybrid working model with flexibility for onsite and remote work.
  • Flexible working hours.
  • Additional paid vacation days, increasing with tenure.
  • Private health insurance package with unlimited and fully paid sick leave.
  • Thoughtfully designed onboarding program with mentorship.
  • Experienced seniors to work with.
  • Dynamic and challenging end-to-end projects.
  • New technologies in action.
  • Possibility to switch projects and technologies.
  • In-house library, training and lectures.
  • HR support and ongoing training for up-and-coming Team Leads.
  • English language lessons.
  • Support for new parents including fully paid maternity leave (in the amount of last salary) and reduced working hours for new mothers and fathers.
  • State-of-the-art macOS devices provided, regardless of location.
  • Bonuses for exceptional performance and employee referrals.

e-Mobility Project

Our Services

System architecture, Software development, project management, consulting.


Kotlin, JavaScript, TypeScript, React, Next.js, and Docker.


IoT, Renewables, Energy storage, Carbon management, Electric mobility.


We are expanding our team to support a client pioneering sustainable energy management. Leveraging a mix of established and cutting-edge technologies such as Kotlin, JavaScript, TypeScript, React, Next.js, and Docker, we are crafting a robust system to be utilized by a large global user base.


Solutions for IoT, renewables, energy storage, carbon management, and electric mobility.

What you are expected to do

  • Working on a project that will be used by a large number of users, where high performance and scalability are standards that are constantly in mind.
  • Analyzing the system and suggesting improvements on the architecture level.
  • Leaving an impact on the project itself.
  • Participate in building a new team from the beginning.

What we look for

  • Backend engineer who is both enthusiastic and willing to deal with various cutting-edge technologies.
  • University degree in computer science (or equivalent).
  • At least three years of experience in any of the following languages: Java, Kotlin, C#, Python, or similar.
  • At least three years of experience in any of the following frameworks: Spring, Quarkus, .NET Core, Flask, or similar.
  • Experience in relational database systems.
  • Experience in Docker and Kubernetes.
  • Experience in Kafka is a plus.
  • Experience working with Cloud platforms and services (Azure, AWS, or GCP) is a plus.
  • Experience in microservices or service-oriented architecture (SOA) is a plus.
  • Experience in distributed systems is a plus.
  • Experience with managing and mentoring Junior Developers.

If interested

Usual way: send your CV to