Lead Backend Engineer

The Role

You'll own the architecture of the Tonsser platform as we move into this next phase. That means making the foundational technical decisions for a product used by a generation of athletes and setting the bar for how a small, ambitious team builds in 2026.

This is a hands-on lead role. You'll write code, shape the system, and set the technical direction. You'll also help us level up as a team, particularly around how we adopt AI as a core part of how we build and what we ship.

What you'll do

• Lead the architectural direction of our backend platform as we evolve from where we are today toward what's next
• Drive the technical roadmap for our new flagship project
• Set the standard for how the team works with AI, both in our development workflow and as a product capability
• Ship production code, review PRs, and mentor the engineers around you
• Partner closely with product, mobile, and design to turn ambitious ideas into things that actually work at scale
• Make pragmatic calls about what to keep, what to evolve, and what to rebuild

Our current stack

• Ruby monolith with a GraphQL API
• SQL (PostgreSQL)
• Hosted on Heroku
• Native iOS and Android apps, with the ambition to move to Kotlin Multiplatform

• We're not dogmatic about the stack, we're looking for someone who can help us decide what stays, what changes, and what comes next.
• What we're looking for

• Significant experience as a senior or lead backend engineer, ideally with time spent owning architecture decisions in a production environment
• Deep comfort with at least one of Ruby, Python, Elixir, Go, or a similar modern backend language, and the judgement to know when language choice matters and when it doesn't
• Strong opinions on API design, data modelling, and system evolution
• Hands-on experience integrating AI/LLM capabilities into real products, or a strong, demonstrable interest in doing so
• Experience leading or mentoring other engineers
• Comfortable working remotely across European timezones
• Bonus: experience with consumer-scale mobile backends, GraphQL, or Kotlin Multiplatform

The shape of the role

• Location: Remote, anywhere in Europe
• Engagement: Open to starting as a freelance contract, with the clear intention of moving to a permanent role
• Compensation: €80,000–€90,000, with flexibility based on experience

• How to apply
• Send us a short note about what you've built, what you're looking for next, and why this caught your eye. We read every application.