Senior Backend Engineer (f/m/d)

At Moss, we give finance professionals the power to automate their day-to-day and make forward-thinking decisions.

Our culture is what makes that possible: we play to win, we obsess over quality, and we win as One Moss, and it works. Moss closed a €35 million Series C in August 2026, crossing a €1 billion valuation, and became one of Europe's fintech unicorns. Join us for what's next.

We are looking for Senior Backend Engineers (f/m/d) for a variety tribes in Warsaw.

Collaborating closely with designers, product managers and frontend engineers, you will bring innovative ideas to life, helping us build the Finance AI platform for Europe's mid-sized businesses.

Your responsibilities

Here's a bit more on what you can expect to be doing day-to-day:

• Backend Development: Lead the development of the application, ensuring it aligns with the product requirements and meets performance and usability standards. Proactively provide regular updates on work progress, achievements and challenges to product managers (PMs) and designers.
• Collaborative Planning: Partner with PMs and designers during project kick-offs to gain a comprehensive understanding of the overall vision, user needs, and goals. Provide valuable insights to refine UI/UX concepts and contribute to the planning of backend development.
• Frontend Collaboration: Collaborate closely with frontend engineers to determine required APIs and frontend functionality. Maintain clear communication channels to ensure smooth integration of frontend and backend components.
• Testing and Quality Assurance: Produce well tested and reliable code. Writing unit and functional (end-to-end) tests.
• Rollout and Performance Monitoring: Collaborate with product managers to devise efficient rollout strategies for new features. Monitor performance and user feedback to identify areas for improvement and proactively address potential issues.

About you

We think you’ll need the following experience and qualifications to succeed in this role:

• Proven experience as a Backend Engineer, leading projects end-to-end to launch.
• Proficiency in Java development technologies (incl. Spring framework), as well as latest features and best practices such as microservices, message queue, alerting, reliability and feature flags.
• Understanding of development design patterns and techniques, incl. Rest API design principles.
• Hands-on experience with testing approaches and libraries (unit testing, integration testing).
• You are fluent in English.

In addition, here are the skills and attributes we are looking for:

• Pragmatic Tech Enthusiast: You have the theoretical and practical background to engineer our product. You pursue quality and scalability and follow industry and company best practices. You build systems that are easy to maintain and to understand by others.
• Delivery Focused: You understand and focus on what is important to deliver the most impact. This means accurate development and delivery estimations, ruthless prioritization and saying no to less important things. You are driven to deliver tangible outcomes within estimated timelines, and you swiftly tackle challenges, and provide clear direction to others.
• Collaborative Communicator: You convey information effectively to a variety of audiences, and actively participate in daily meetings, keeping others informed about your progress and status. You’re able to form trustworthy connections by creating and maintaining open communication with colleagues throughout the development process.
• Inquisitive Mindset: You’re detail-oriented and seek to develop a deep domain knowledge by proactively seeking to understand workflows and technical intricacies. You’re curious and unafraid to question assumptions and propose alternative approaches, ensuring the product is tailored to meet customer needs.
• Team Player: You bring a team together to work towards a shared goal, as well as support individuals throughout all phases of a project.

About Moss

Moss is the Finance AI platform for Europe's mid-sized businesses, giving companies real-time visibility and full control over their spend. By automating card issuing, invoice management and expenses, Moss simplifies financial workflows and frees finance and accounting teams from manual, administrative work.

Founded in Berlin and used by more than 10,000 businesses including Flink, Schufa, n8n and Auto1, Moss has raised €220+ million to date and operates in Germany, the Netherlands, the UK and further EU markets. In August 2026, Moss closed a €35 million Series C led by Portage, crossing a €1 billion valuation and becoming one of Europe's newest fintech unicorns. Moss is backed by investors including Valar Ventures, Tiger Global, Global Founders Capital, Cherry Ventures, A-Star.

We're a team of 300+ people from 50+ nationalities across 5 offices in Europe and we hire, reward, and grow people based on Moss DNA: playing to win, obsessing over quality, winning as One Moss. If that's how you want to work, we want to hear from you. - here's what else to expect:

• Top-of-market compensation package, including equity.
• Our vibrant offices are at the heart of our culture, where in-person time fuels collaboration and connection over weekly breakfasts and Friday demos.
• Additional benefits include: 20 days “work from abroad”, 600EUR/GBP Learning & Development Budget, and other local benefits.

Unless stated otherwise, benefits apply to full-time positions (interns and working students receive a tailored package).

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