Junior Backend Engineer – Building Smart Cities with Code

Who We Are

We are a Sofia based company and care about the city we live in. At Theoremus, we have a common vision that we want to share and live in cleaner, healthier, happier and better cities overall, and we know that to live this dream today means we have to combine skills, reason and passion in a bold, new way.
We’ve gained expertise and are currently focused on two main areas:

• Mobility аnalytics & ticketing – We pride ourselves in developing Sofia’s public transportation ticketing system, and especially its online components, such as the QR tickets and the debit card payments. Furthermore, on top of that, we have developed its advanced analytics sub-system, which measures the behavioural patterns of public transit passengers, and aims to optimise for a frictionless experience. Our goal is to continuously enhance user experience and encourage people to limit the use of private vehicles, and thus improve urban mobility, traffic and air quality in the cities where your friends and family live.
• Smart waste management – Our know-how in the waste management sector has been disseminated into multiple projects throughout Bulgaria and Spain. We have developed big IoT systems consisting of thousands of sensors attached to trucks and containers. The aim of these systems is to deploy data science methods in order to optimise the circular economy lifecycle and make waste taxation fairer.

What We’re Looking For

We know you might not have years of experience yet, but what matters is your curiosity and willingness to learn. Here’s what we’d love to see:

• Familiarity with backend development in Go, Python, Java, or similar languages.
• Understanding of how APIs and databases work (PostgreSQL, MongoDB, or any other).
• Interest in event-driven architectures, stream processing, or cloud technologies (bonus points if you’ve heard of Kafka, Kubernetes, or Docker).
• A healthy relationship with change – We know that code can feel like your baby, but sometimes even the best solutions need a little tweaking. We’re looking for someone who embraces iteration and understands that today’s code might need a small refactor tomorrow to become even better.
• Passion for AI and machine learning – whether you’ve worked on AI projects or simply have a strong interest in how AI shapes the future, we want to hear from you.
• A problem-solving mindset – we love people who ask why before jumping into a solution.
• Eagerness to learn, experiment, and grow – technical expertise can be developed, but curiosity and motivation are priceless.

What You’ll Learn

You’ll gain hands-on experience working on real-world backend systems that impact thousands of people every day. You’ll learn:

• How to build scalable and efficient backend services for urban tech solutions.
• How APIs, microservices, and cloud infrastructure work together.
• How to handle real-time data and connect backend services to large IoT networks.
• How modern data-driven platforms support AI and machine learning processes.

What You’ll Do

• Develop and improve backend services that power our mobility and waste management platforms.
• Work closely with front-end developers, data scientists, and IoT engineers to bring new features to life.
• Contribute ideas and solutions – if you see something that can be better, we want to hear it.
• Improve system performance and reliability, ensuring smooth data flow between different components.
• Learn from senior engineers and grow in a supportive team.

What We Use (You Don’t Need to Know It All!)

• Languages: Go, Python
• Databases: PostgreSQL, MongoDB, Apache Cassandra
• Tools & Platforms: Apache Kafka, Kubernetes, Jenkins, Apache Airflow, Grafana, Prometheus
  We don’t expect you to know all of these – you’ll have the chance to learn on the job.

What We Offer

• Competitive salary and real career growth in an innovative company.
• Additional health insurance and Multisport card to keep you healthy.
• Public transport card – because we believe in sustainable mobility.
• 25 days of annual paid leave – because we know rest is important.
• Fridays that end at 2 PM – because balance matters.
• A team that values learning, creativity, and having fun together.
• An amazing office in Sofia’s city center with a 360-degree panoramic view and a summer terrace for coffee, networking, and cake (we love cake).
• A mission that matters – your work will improve city life for thousands of people.

What We Believe In

We don’t just write code – we build systems that make cities smarter. Part of our values:

• Services over monoliths – Keep things modular and scalable.
• Prototyping before development – Test before committing.
• Science over technology – Data-driven decisions over hype.
• Trust over processes – You get ownership, not micromanagement.
• People and sustainability first – Tech should serve people, not profits alone.
• AI as a tool to eliminate repetitive coding tasks – so our team can focus on solving complex, meaningful problems that drive innovation.

That’s the short version. We know we’re not alone on this journey.

How to Apply?

If this sounds like the kind of place where you’d love to grow, let’s meet 🙂

Send us your CV and GitHub (or a project you’re proud of).

If you don’t meet all requirements but you’re excited about what we do, apply anyway – we care about potential, not just experience!