Senior/Lead Backend Engineer – AI / HR Tech (Category-defining European Startup)
We’re not just building another HR tool. We’re building the intelligence layer that helps thousands of teams think, decide, and grow smarter. This is your chance to build from the ground up, not just maintain what already exists.
Join us as our Senior/Lead Backend Engineer and shape the AI core that will power the next generation of work. This is a full-time, remote-first role. The compensation range is €4,500–€6,000 monthly.
👋 Meet Sloneek
We’re Sloneek, a fast-growing European HR tech startup on a mission to change HR for the better. Our platform helps organizations run smoothly — managing people, data, and workflows with clarity, accountability, and a touch of AI magic.
We’re 35+ people across Europe, working hybrid and remote, and gearing up for our next growth round. We build HR “superhuman” experiences for customers including Lindt, Sky, Carvago, Volvo, Čedok, Košík, and Kontentino. Tech, people culture, and real product impact belong together here.
🧠 Your playground: backend, AI and real product impact
You’ll work in a modern, AI-powered backend environment that blends reliability with cutting-edge experimentation. You’ll design the architecture behind AI-assisted HR workflows, connecting structured data, human actions, and intelligent automation into one seamless experience.
Backend: Python 🐍 is our core backend language, with FastAPI ⚡ for high-performance, async-ready APIs.
Data: PostgreSQL gives us a relational, scalable foundation — with some JSONB magic where it makes sense.
AI layer: We use LLM-based agents with OpenAI and Anthropic models for automation, reasoning, and HR insights.
Agent integrations: You’ll experiment with Model Context Protocol (MCP), powering next-gen integrations between agents, live company data, and user actions.
Infrastructure: Kubernetes, Docker, AWS, and Bitbucket/GitHub Actions support reliable delivery and scale.
Monitoring: We work with Prometheus and Grafana — or alternatives you can help define.
💪 What you’ll actually be doing
Build the core: Design and build the Python/FastAPI backend behind Sloneek Intelligence — the AI layer of our HR product, running in production for real customers today
Put AI into production: Turn LLM APIs (OpenAI Responses API, reasoning models, MCP) into reliable product features — how models query real company data, how we evaluate them, how we keep latency, token budgets and failures under control
Connect the product: Design the APIs that link the intelligence layer, the core HR platform, data services and the frontend
Ship with context: Work directly with product and design on features that make HR work faster — small senior team, you own your decisions
Set the bar: Define standards for clean code, performance, and data security as we scale
✅ You might be a fit if you…
Know Python deeply: Ideally, you’ve worked with async frameworks such as FastAPI or Flask.
Are comfortable with PostgreSQL: You know how to design and evolve data models that support a real product.
Have built RESTful APIs: Not toy projects — APIs that power products people genuinely use.
Are AI-curious: AI agent design, prompt orchestration, and workflow automation interest you, even if you’re not an ML researcher.
Care about clean architecture: You think about how systems evolve, not only how they run today.
Thrive in ownership: You’re proactive, communicative, and comfortable in fast-moving environments where decisions are owned, not passed around.
❌ You're not a fit if your AI experience is demos and prompt glue, or if you're an ML researcher looking for a research role. This is hard backend engineering where the hardest component happens to be an LLM.
🌿 Why joining Sloneek makes sense
Real influence: Expect autonomy, visibility, and impact — without corporate layers
Space to innovate: We make time for innovation, learning, career growth, and trying better ways of working
Flexibility that works: Remote work, home office, flexible hours, sick days, extra holiday, and a healthy work-life balance
Tools and team: Laptop, Multisport card, relax zone, education budget, teambuildings, and a friendly professional team
Culture: Accountability, challenge, creativity, and good humor are all part of the package
✉️ Ready to build the intelligence layer?
If you’re passionate about backend architecture, AI integration, and building from zero with real impact, we’d love to hear from you.
After you apply, we’ll get back to you within a few days. First, we’ll have a relaxed chat to align expectations; then we’ll dive into your technical experience, discuss architecture and AI challenges, and introduce you to the people you’ll work with.
Let’s reinvent HR together — one smart API at a time. Apply now, we’re looking forward to meeting you.