Senior Java/Kotlin Engineer (Freelancer)

We’re looking for a Senior Java/Kotlin Freelancer with at least 3 years of Kotlin backend development experience to join a renewable energy trading project. The solution connects asset data and trading operations on a single platform, enabling end-to-end automation across forecasting, trading, and dispatch.
You’ll work with Kotlin and Spring Boot in a full Supercharge project, with design, project management, architecture, and tech leadership provided in-house. The team works in Hungarian, while specifications are in English, and there is no direct client interaction.
The project runs full-time (40 hours/week) for approximately 3 months, with an expected start in mid-November.On-site presence is required once a week at our Budapest office (Czuczor utca 2., 3rd floor), with additional days possible if needed.
You can expect a high-quality engineering environment focused on clean code, modern technologies, a strong team, and a friendly atmosphere.

Your day to day will include:

- Supporting the development of a stable and scalable Kotlin and Spring Boot back-end from the ground up

- Crafting code that adheres to the highest industry standards while ensuring seamless integration with our Cl tools

- Collaborating effectively within a dynamic team environment on exciting, cutting-edge tech initiatives while working closely with fellow engineers and supporting Tech Leads and Architects

- Bringing an architectural perspective to the planning process

What makes you thrive here:

- 3+ years of experience in Java ecosystem, familiarity with Java 17, 21

- Deep understanding of Spring Boot

- Experience with an observability platform (Grafana / LGTM or ELK stack or NewRelic)

- Proven ability to troubleshoot under pressure, quickly identify root causes, recommend impactful solutions, and ensure thorough follow-through

- Hands-on experience with SQL or NoSQL databases (Postgres, Redis)

- Experience with Kubernetes

- Familiarity with at least one public cloud provider (preferably AWS)

- Familiarity with IaC, such as Terraform, Helm is a plus

- A strong OOP mindset and a commitment to upholding SOLID principles

- A passion for writing clean, maintainable code, adhering to best practices (if you're a Clean Code/Coder/Architecture fan, you're more than welcome)

- Kotlin experience is a huge plus, as this is our choice of language on the JDK

- At least an intermediate level of English language skills since our team operates internationally

Who are we?

- Supercharge is one of the fastest-growing tech companies globally, according to Financial Times (FT1000) and Deloitte (EMEA Fast500). Our in-house team of over 200 digital experts across our European and North American offices are passionately united in the pursuit of discovering and building better futures.

- We cut through business, tech and regulatory complexity and fuse Behavior Science-based design and unique data & AI-focused technical competence to propel your business. We believe that innovation is a team effort: our strategists, designers, developers and engineers work shoulder to shoulder to enable what yesterday was still impossible.

About our Budapest office

Budapest is where it all started for Supercharge - this is our headquarters and the beating heart of our company. We have local offices in several countries, but this is where the real magic happens. A buzzing, vibrant space filled with talented individuals dreaming up and delivering amazing products for our clients. This Office of the Year award-winning space is home to our legendary after-work events, and as located in the heart of the city, putting us just steps away from some of the best restaurants, cafes, and bars around.