Senior Software Engineer - FullStack

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 users (and affiliates) for sharing the product 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 - FullStack (m/f/x) to help us realize our committed vision.

Your Mission

⭐ Our team is looking for a Senior Software Engineer - FullStack (m/f/x) who will help us further develop, challenge and improve our existing product. This is a unique growth opportunity to demonstrate your knowledge and expertise and help create a product to change the way B2B SaaS solutions sell their products.

TL;DR

🌱 Seed, GrowthTech, runway 24 months

🌎 Remote-First (+/-3 CET)

🍰 Competitive base salary + eVSOPS

🚀 Why join

• Unique growth opportunity: early-stage GrowthTech start-up backed by top-tier investors ($8.3M total funding).

• Complex and interesting product: APIs, attribution models, recommendation engines, and more.

• Strong momentum: SaaS companies need cost-effective sales channels → we’re the solution.

• Build the engineering culture you’d recommend to your ex-colleagues.

• We onboard 15+ new customers every month and already reach 6M+ monthly users.

• Work with an experienced founding team (ex-Twilio, Pitch, Typeform).

🏔️ What we're building

We help SaaS companies turn users into their best sales channel.

Our platform powers referrals, sharing & recommendations — used by millions monthly.

Tech stack includes:

• Frontend widgets embedded into customer apps.

• High-performance APIs for seamless integrations.

• Full customer portal for managing campaigns & analytics.

Under the hood: attribution models, recommendation engines, scaling millions of events — much more than a simple web app.

⭐ Your responsibilities

• Stack: React · NestJS · Python · AWS

• Work directly with stakeholders — no walls, no ticket factory.

• Build new features and improve existing systems.

• Pragmatic balance: Sometimes we ship fast to learn, sometimes we slow down to fix the foundation — you’ll help decide where to lean.

• Have real influence on architecture and product direction — not just coding tickets.

  
  

About You

🛠️ We value diverse backgrounds and encourage you to apply even if you didn't follow the traditional career path. We're always looking for individuals who can bring a new perspective to the table.

Required

• Good communication skills and a friendly, collaborative attitude

• Good English skills (written & spoken)

• You know when “good enough” is right — and when to invest in quality

• Solid experience: React or similar, NestJS/Python or similar, and AWS is a must

• Comfortable debugging complex problems

• Contribute ideas, challenge assumptions, shape solutions

• Use AI tools wisely but don’t depend on them

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.

• Competitive, adjustable compensation based on your appetite between equity/cash

• vESOPs based on the generous Index Ventures guidelines, which sets us apart from most European startups

• Remote-first global company with local hubs. We hire the best, senior people regardless of location

• Flexible office allowance to support your hybrid or fully remote working model

• Build your perfect setup to do the best work of your life. Mac/Windows, plugins, cutting-edge tech stack… Tell us what you need to be productive and we will take care of it

• Monthly learning allowance to satisfy your thirst for growth and lifelong learning

• Regular culture weeks where we come together, celebrate and set the course for the coming months. We have chosen to work remotely, but we encourage frequent face-to-face time