Senior Software Engineer (m/f/d)

About this role

Cello is the Revenue Growth Infrastructure for modern digital businesses. We help teams acquire, retain, and monetize customers at scale by turning word-of-mouth into a systematic, measurable growth channel - built for the AI era.


We’ve raised $10.3M total funding led by top-tier investors, and we’re now looking for a Senior Software Engineer - Full Stack (m/f/x) to help us realize our committed vision.

# TL;DR

• Seed, GrowthTech
• Remote-first, Europe-based (must be within CET +/-3 hours)
• Competitive salary + eVSOPS

Why join

• GrowthTech scale-up with **$10.3M in funding** from top-tier investors.
• Exciting product: APIs, attribution models, MCP integration, AI-based recommendation engines, and assistants - not your typical CRUD app.
• Real traction - **30+ new customers every month**, **10M+ end users monthly**.
• Small team, so you'll genuinely shape how we build things.
• You'll touch everything from frontend widgets to backend infrastructure to data pipelines. The work doesn't get repetitive.
• We actively learn about new tech and AI tools and adopt where we can — we have to, because our customers do.
• Remote-first, but we get together regularly - company-wide and as an engineering team.
• The founding team consists of serial founders and experienced big-tech operators from **Twilio, Wise, and Skype**.

# What We’re Building

We help SaaS companies turn their users and partners into a sales channel through referrals, sharing, and recommendations - 10M+ end users interact with our system every month.

Our widgets live inside customer products, which means your code runs in environments you don't control. On top of that: APIs that customer developers integrate against, and a portal where customers manage their campaigns and analytics.

Under the hood: attribution across complex user journeys, AI-based recommendation engines, multi-tenant infrastructure serving hundreds of customers, scaling millions of events. Dee...