About the role
This Senior Software Engineer - Full Stack role joins a small, remote-first European team at Cello building referral and recommendation systems used by 10M+ end users per month; you’ll work across widgets, APIs, and backend infrastructure to influence product direction, architecture, and how we adopt AI to ship faster. This role matters because your decisions will shape a multi-tenant platform that runs inside customer products and integrates with a wide variety of developer workflows.
What you'll do • Collaborate directly with stakeholders to define and deliver features without a ticket factory. • Build new features and improve existing systems across frontend, backend, and data pipelines. • Decide when to ship fast for learning and when to slow down to strengthen the foundation. • Influence architecture and product direction beyond executing tickets. • Help adopt and integrate AI-driven tooling and agentic coding approaches into our engineering workflow. • Work on frontend widgets that run inside customer products, APIs for integrators, and a customer portal for campaign management. • Design for attribution across complex user journeys and scale multi-tenant infrastructure handling millions of events. • Ensure our product fits diverse developer workflows from corporate teams to solo founders using AI agents. What Cello is looking for • Strong experience with React (or similar) for frontend work and NestJS/Python (or similar) for backend services. • Proven AWS experience building and operating cloud infrastructure. • Familiarity with mobile development (React Native, Flutter, etc.). • Experience with data warehousing / analytics (e.g., Snowflake, ClickHouse, or similar). • Excellent communication skills and a collaborative attitude. • Strong problem-solving skills: break down ambiguous problems and ship pragmatic solutions. • Ability to judge trade-offs between shipping quickly and investing in quality. • Ownership mindset: reliable, strong work ethic, and proactive contributor of ideas. • Deep curiosity about product and developer workflows, and hands-on experience pushing AI coding tools to their limits while still understanding core system behavior.