Founding Fullstack Engineer @Rose

🚀 Hexa
Rose is a startup launched by Hexa, the Paris-based startup studio founded in 2011 that has created over 40 companies including Front, Aircall, Spendesk, and Swan (3 unicorns, +$700M raised, portfolio valuation >$5B).
With €29M in funding finalized in 2025 and the goal to launch 30 startups per year by 2030, Hexa offers a unique environment: shared resources, expert network, and an ecosystem of hundreds of engineers and founders.

🎯 Rose in a nutshell
The problem: 85% of B2B website visitors leave without interaction. Meanwhile, they use ChatGPT and Perplexity to compare solutions before even contacting you.
Our mission: Transform B2B websites into intelligent conversational assistants that engage 100% of traffic, capture quality zero-party data, and increase demo conversions.
Our approach: Unlike traditional chatbots (~5% engagement), Rose achieves 20%+ engagement through an integrated assistant experience, not an intrusive popup.
Our clients: Pennylane, Mayday, AB Tasty are already using Rose in production.

💼 The role
You'll join Rose as the first Founding Engineer to build the platform alongside, Benoit, CTO/Cofounder.
You'll work on cutting-edge technical challenges in an environment where every line of code has a direct impact on the product and users.

Your missions:
• Architecture & Development
Co-build the technical architecture with the CTO (backend, frontend, infrastructure)
Develop core features: conversational AI engine, interactive experiences, third-party integrations, back-office
Make technical choices that structure the platform for the next 5 years

• AI & Performance
Participate to the implementation of RAG (Retrieval-Augmented Generation) systems in production with Vector database and knowledge graph
Optimize real-time performance
Develop guardrails and testing mechanisms to ensure AI response quality

• Integrations & Product
Build bidirectional integrations with CRMs (Salesforce, HubSpot)
Orchestrate calendar systems (Calendly, Chili Piper) and analytics (Posthog)
Participate in product decisions and user exchanges

Tech Stack:
• Backend: Python, Fast API, PostgreSQL, MongoDB Vector Database, Neo4j
• Frontend: React, TypeScript AI/ML: LLMs, Vector embeddings, prompt engineering, Langgraph
• Infrastructure: GCP, GitHub Actions, monitoring and observability

Tech Philosophy:
• We favor pragmatism over theoretical perfection, iteration velocity over over-engineered architectures, and user impact over technical elegance. You'll work in an environment where we ship quickly, test with real users every week, and learn constantly.

👤 Who we're looking for:
• 4+ years of experience in fullstack development on B2B SaaS products
• Mastery of React/TypeScript on the frontend and a modern backend framework
• Experience with Python
• Experience with SQL and NoSQL databases, REST or GraphQL API design
• Ability to define technical architectures and challenge design decisions
• Experience deploying and monitoring applications in production

Mindset:
• Builder first: you prefer building and iterating rather than debating for hours
• Product-minded: you think about user impact before technical elegance
• Ownership: you make decisions, own the results, and adjust
• Adaptability: you're comfortable with ambiguity and pivots of an early-stage startup
• Technical curiosity: you love learning (generative AI, for example, even if you're a beginner)

Nice to have:
• UX and design sensibility
• Experience with complex third-party integrations (CRM, analytics, calendars)
• Experience with generative AI or LLMs
• International or multilingual context

🎁 What we offer:
• Competitive salary aligned with the senior engineer market in Paris
• Lastest Macbook Pro
• Premium health insurance (Alan or equivalent)
• Joining a renowned startup studio: you’ll be in a dynamic environment, surrounded by smart and ambitious people in a fun atmosphere
• Lovely offices at Hexa, in Paris (75010)
• Hybrid remote: 2 days a week in the office, the rest is up to you

Recruitment process

We respect your time with an efficient ~3 week process:
- Discovery HR interview (30 min) - Rose presentation, discussion about your background
- CTO interview (45min) with the CTO - Discussion about your experiences, technical approaches
- Tech assessment (2-3h max) - Realistic technical problem related to our challenges (remote possible)
- Final meeting (2h) at the office - Technical deep dive, culture fit with Johary, CEO & Florent, Partner Hexa
- References and formal offer