Senior Backend Engineer

About Lago At Lago, we're on a mission to make billing simpler, more transparent, and more adaptable for SaaS companies. As the leading open-source billing platform, we empower businesses to build flexible pricing models and scale with confidence. We've raised over $22 million in funding from top-tier investors including Y Combinator and FirstMark, reflecting strong confidence in our vision and growth. Our platform has garnered over 9,000 stars on GitHub, a testament to our active and growing developer community. Companies such as PayPal, CoreWeave, Synthesia and Mistral.ai choose Lago for their billing. We're a team of ambitious, focused individuals who work together to solve hard problems with excellence and accountability. At Lago, we value reliability and proactivity—we trust each other to own tasks, drive them to completion, and adapt quickly. While we encourage you to try fast and "fail fast", we also expect you to learn fast: make mistakes, but don't make the same one twice. If you're excited by challenges and want to grow alongside a high-performing, supportive team, this is the place for you.

Overview

We're looking for a Senior Backend Ruby Engineer to contribute to Lago's core product and help scale our open-source billing infrastructure. You'll work across the full backend stack, collaborate closely with Product and Frontend, and help shape how we build and evolve the platform. What You'll Be Doing Contribute daily to all parts of our codebase, using our development workflow Tackle a wide variety of technical problems throughout the stack Help grow the back-end team Work with our Product Team and Front-end Engineers to understand customer needs and challenges Come up with technical solutions to create and improve our best features and architecture Who You Are Strong knowledge of Ruby (at least 6 years hands-on experience) Experience working with large volumes of data and event-driven environments A genuine passion for Open-Source: if you've contributed to OSS projects or used OSS tools, let us know! A real appetite for the early stages of co-creating a product and shaping Lago's future Bonus: you've worked on billing or tax projects — whether implementing a billing system, maintaining it, or integrating it with business tools (e.g. a CRM, Finance tools) Who You're Not You're not looking for a "just ship it" culture without quality standards — we care deeply about both speed and craftsmanship You're not someone who works in silos — you actively collaborate with Product, Frontend, and your fellow engineers You're not intimidated by ambiguity — early-stage problems don't always come with a clear spec, and you're comfortable navigating that You're not allergic to context-switching — in a lean team, priorities shift and you adapt without losing momentum Requirements 6+ years of hands-on experience in software engineering, with strong Ruby expertise Experience working with event-driven systems and high-data-volume environments Familiarity with background job frameworks (e.g. Sidekiq) and message queues Comfort with REST APIs, webhooks, and data integrations Strong written and verbal communication skills A mindset of ownership, curiosity, and resilience Nice to have Experience contributing to or supporting open-source projects Familiarity with billing systems, fintech, or developer tools Experience with PostgreSQL, Redis, Kafka, or similar infrastructure Exposure to containerised environments (Docker, AWS, CI/CD) Why Join Lago? Work with top-tier talent: Join a team that values excellence, ambition, and accountability Shape the future of fintech: Be part of a fast-growing company building the best open-source billing platform Remote-friendly: Work from anywhere in Europe (within +2h/-2h of CET), or join us in our Paris office Competitive package: Competitive salary and equity for employees based in France Make an impact: Your work directly shapes the product used by companies like PayPal, Synthesia, and Mistral.ai Ready to Build with Us? If you're excited about joining a high-talent team to solve meaningful problems and help businesses thrive, we'd love to hear from you. Apply today and let's build something remarkable—together. Location type: Remote Primary Location: Remote Europe Team: Product Engineering Work Type: Full Time/Permanent Contract Salary: 70,000–100,000 EUR per year (Applicants must be based in the location specified for this role. Applications from other locations will not be considered.)