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**](http://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](http://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.)_