Senior Software Engineer (m/f/d)
Cello
Job Description
<h1><strong>🚀 Why join</strong></h1><ul style="min-height:1.5em"><li><p style="min-height:1.5em">AI-powered infrastructure company with <strong>$10.3M in funding</strong> from top-tier investors.</p></li><li><p style="min-height:1.5em">Exciting product: APIs, attribution models, MCP integration, AI-based recommendation engines, and assistants - not your typical CRUD app.</p></li><li><p style="min-height:1.5em">Real traction: <strong>30+ new customers every month</strong>, <strong>10M+ end users monthly</strong>.</p></li><li><p style="min-height:1.5em">Small team, so you'll genuinely shape how we build things.</p></li><li><p style="min-height:1.5em">You'll touch everything from frontend widgets to backend infrastructure to data pipelines. The work doesn't get repetitive.</p></li><li><p style="min-height:1.5em">We actively learn about new tech and AI tools and adopt where we can — we have to, because our customers do.</p></li><li><p style="min-height:1.5em">Remote-first, but we get together regularly - company-wide and as an engineering team.</p></li><li><p style="min-height:1.5em">The founding team consists of serial founders and experienced big-tech operators from <strong>Twilio, Wise, and Skype</strong>.</p></li></ul><h1><strong>🌟 What We’re Building</strong></h1><p style="min-height:1.5em">We help SaaS companies turn their users and partners into a sales channel through referrals, sharing, and recommendations - <strong>10M+ end users</strong> interact with our system every month.</p><p style="min-height:1.5em">Our widgets live inside customer products, which means your code runs in <strong>environments you don't control</strong>. On top of that: APIs that customer developers integrate against, and a portal where customers manage their campaigns and analytics.</p><p style="min-height:1.5em">Under the hood: attribution across complex user journeys, AI-based recommendation engines, multi-tenant infrastructure serving hundreds of customers, scaling millions of events. Deeper than you'd expect from a referral tool.</p><p style="min-height:1.5em">Our product is integrated by customer developers - and that world is changing fast. The people building against our APIs and widgets range from <strong>corporate engineering teams to solo founders using AI coding agents</strong>. Keeping up with how developers work today, and making sure our product fits into all of those workflows, is one of the more interesting challenges here.</p><p style="min-height:1.5em"></p><h1>Your Mission</h1><ul style="min-height:1.5em"><li><p style="min-height:1.5em"><strong>Stack:</strong> React · NestJS · Python · AWS</p></li><li><p style="min-height:1.5em">You work directly with stakeholders - no walls, no ticket factory.</p></li><li><p style="min-height:1.5em">Build new features and improve existing systems.</p></li><li><p style="min-height:1.5em">Sometimes we ship fast to learn, sometimes we slow down to fix the foundation - you'll help decide where to lean.</p></li><li><p st
Skills