Senior Software Engineer (Java / Kotlin)

About the role

Addendum, a global software development and IT team augmentation firm focused on fintech, banking and telco, is hiring a Senior Software Engineer in Tallinn, Estonia. You will join a team of experienced IT professionals working on a securities trading project in the banking sector, with a focus on trading automation, system integrations and backend development. The role is hybrid and requires candidates to be based in Tallinn; the earliest start date is 16 November 2026.

Key responsibilities

• Design, develop, test and document backend functionality for the Trading Automation project.
• Build secure, scalable and maintainable solutions using Java or Kotlin, Spring Boot and REST APIs.
• Build and enhance system integrations within an existing application landscape.
• Work with relational databases, including data modelling, SQL development and query optimisation.
• Translate business requirements into technical solutions and make sound architectural and design decisions.
• Take ownership of project deliverables and ensure high-quality implementation within timelines.
• Collaborate with business stakeholders, developers, architects and other technology teams.
• Participate in code reviews, testing and technical documentation.

Required profile

• Extensive professional experience in backend software development, with a proven track record of complex, integrated or business-critical systems at a senior level.
• Proven ability to turn business requirements into secure, scalable and maintainable solutions.
• Hands-on experience building system integrations and implementing changes in existing enterprise applications.
• Strong understanding of software engineering best practices, clean code, code reviews and technical documentation.
• Ability to manage deliverables independently and take responsibility for solution quality.
• Excellent English communication skills.

Required skills

• Strong expertise in Java or Kotlin, Spring Boot and API design and development.
• Solid experience with relational databases, SQL and query optimisation.
• Nice to have: Angular or other frontend technologies, and experience in securities trading, investment services, banking or financial markets, including securities settlement and trading automation.

What we offer

• Competitive market-based remuneration under a B2B contract or a regular employment agreement, tailored to experience and expertise.
• Personalised benefits packages, plus automatic perks such as collaboration with award-winning international teams, diverse projects, team events, learning and development opportunities and celebrations for birthdays and milestones.