Founding Principal Engineer (m/f/d) / Ferto AI

About us

Most labs still count cells under a microscope by hand. It's slow, repetitive, and error-prone. We're replacing that manual work with software. By combining a standard microscope with a smartphone, we run computer vision models that locate, track, and measure cells automatically in real time. We're starting with semen analysis and expanding to other routine microscopic samples. Based in Berlin, we're a small, well-funded team founded in 2026 operating in stealth. Our goal is to make automated, reliable diagnostic analysis accessible on any phone connected to a microscope.

The role

We're looking for an engineer who wants to own the whole platform behind a medical product: services, data, infrastructure, security and identity. A first version runs today. The hard part is making it trustworthy enough for clinical use: patient data that stays safe, an audit trail that holds up for years, and a system that recovers when something breaks. You'll own all of it, working closely with the founders and our CTO.

What you'll do

• Own the platform end to end: backend, data, infrastructure and security.
• Get it ready for clinical use, and keep it reliable as we grow.
• Build identity, access and data handling that clinics and auditors can trust.
• Make the architecture calls: what to build now, what to defer, what to cut.
• Set the engineering standard and help hire the team that follows.

What you bring

• Platforms you've built and run. You've built backend platforms from scratch and run them in production, through outages, data incidents, migrations and growth.
• Database depth. You know what happens under the query: indexing, locking, transactions, replication, zero-downtime schema changes, and backups you've actually restored.
• Security by default. Authentication and authorisation, tenant isolation, secrets, audit logging.
• Identity done properly. Identity providers, sessions and tokens, roles and permissions, onboarding and offboarding.
• Infrastructure. Infrastructure as code, containers, Linux, networking and cloud are everyday tools for you.

Beyond the backend

• The backend is your home, but when the product needs it, you read and change the app yourself.
• Systematic troubleshooting. You reproduce first and fix root causes. You work from evidence like logs, traces, metrics and query plans, and you stay calm when production breaks.

AI-native engineering

• Coding agents are part of your daily work. You give them good context, split work into reviewable steps, and stand behind every line you ship.

Ownership

• You help shape the roadmap, push back on weak ideas, set your own priorities and raise problems early.
• Strong opinions, held with evidence and open to revision.

Range

• You've worked across several companies, stacks or environments. How you work counts far more than how many years you've done it.

Nice to have

• Regulated environments with audits: medical devices, health, finance.
• Serving ML models in production.

What we offer

• Ownership from day one. As a founding engineer, you're part of the company through our virtual share option plan (VSOP). You grow with us. You help build the company from the start, and as it grows, your role grows with it.
• Real influence. You decide how we build software, and you shape the engineering team we build.
• A competitive salary. We share the range in our first conversation.
• Flexible hours and office days. We work from Berlin and meet in person regularly, up to several days a week. This isn't a fully remote role.
• English is our working language. German isn't required.
• We sponsor the EU Blue Card if you're moving to Berlin.