Senior Software Engineer - Full Stack

About Us

We believe the future of marketing is word-of-mouth. Our trusted referral platform puts word-of-mouth marketing on autopilot by rewarding end users (and affiliates) for sharing the products they love! The only all-in-one referral platform for B2B SaaS.

We’ve raised $8.3M 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

• Early-stage GrowthTech start-up with $8.3M in funding from top-tier investors.
• Exciting product: APIs, attribution models, recommendation engines - not your typical CRUD app.
• Real traction - 15+ 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.
• Founding team comes 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, recommendation engines, multi-tenant infrastructure serving hundreds of customers, scaling millions of events. Deeper than you'd expect from a referral tool.

Our product is integrated by customer developers - and that world is changing fast. The people building against our APIs and widgets range from corporate engineering teams to solo founders using AI coding agents. 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.

Your Mission

Stack: React · NestJS · Python · AWS

• You work directly with stakeholders - no walls, no ticket factory.
• Build new features and improve existing systems.
• Sometimes we ship fast to learn, sometimes we slow down to fix the foundation - you'll help decide where to lean.
• Real influence on architecture and product direction, not just coding tickets.
• Help us adopt the latest AI improvements to speed up how we build and ship.

About You

Required

• Good communication skills and a collaborative attitude
• Solid experience with React (or similar), NestJS/Python (or similar), and AWS
• Good English (written & spoken)
• You know when "good enough" is right - and when to invest in quality
• Comfortable debugging complex problems
• You contribute ideas and challenge assumptions, not just execute
• You're curious about the product itself - you want to understand what we're building and why, not just pick up tickets and ship code.
• You keep up with the AI tooling landscape and are eager to use what's out there — we move fast on adopting what works.
• That said, you know how code and systems actually work. You can debug, reason about architecture, and carry your weight in a codebase without an AI assistant holding your hand.

Nice-to-haves

• Experience with mobile development (React Native, Flutter, etc.)
• Familiarity with data warehousing / analytics (e.g. Snowflake, ClickHouse, or similar)

Benefits

In the end, it’s all about the team and our culture. Understand why we love our job and see what it’s like to work at Cello in our People Playbook. We have some compelling perks and benefits.