Senior Java/Kotlin Engineer (Freelancer)

Our vision is simple yet powerful: we want to create a place where engineers thrive, taking on exciting projects and using the latest technologies, free from the shackles of legacy solutions.

Thanks to the diverse range of industries we work with, our days are never boring: from world-class apps to AR solutions or even programming robots, we’ve got it all covered. We don’t just write code for our screens; rather, we develop impactful products used by millions every day: let them be large-scale public transport applications, leading fintech platforms, or storage solutions contributing to a greener future.

We are a team of 100+ engineers (Java, JavaScript, Android, iOS, NodeJS and dotnet platforms) and QA engineers with our coding fingers at the ready working on the next big thing. We value openness, modesty, hard work, and simple yet great solutions.

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.