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 missionsArchitecture & 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 StackBackend: 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 PhilosophyWe 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 for4+ years of experience in fullstack development on B2B SaaS productsMastery of React/TypeScript on the frontend and a modern backend frameworkExperience with PythonExperience with SQL and NoSQL databases, REST or GraphQL API designAbility to define technical architectures and challenge design decisionsExperience deploying and monitoring applications in production MindsetBuilder first: you prefer building and iterating rather than debating for hoursProduct-minded: you think about user impact before technical eleganceOwnership: you make decisions, own the results, and adjustAdaptability: you're comfortable with ambiguity and pivots of an early-stage startupTechnical curiosity: you love learning (generative AI, for example, even if you're a beginner) Nice to haveUX and design sensibilityExperience with complex third-party integrations (CRM, analytics, calendars)Experience with generative AI or LLMsInternational or multilingual context What we offerCompetitive salary aligned with the senior engineer market in ParisLastest Macbook ProPremium 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 atmosphereLovely offices at Hexa, in Paris 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