Full Stack Developer
Role details
Job location
Tech stack
Job description
collaboration among passionate professionals working in agile teams. Guided by curiosity and ambition, we strive to create products that are meaningful and impactful, while remaining true to our authentic selves. About the Project We are building a sophisticated, open-source AI conversational platform that integrates multiple AI providers to deliver a rich, cutting-edge user experience. We are looking for an experienced Senior Full Stack Developer to join our core team as a B2 B partner. While this is a full-stack role, your primary focus (~80%) will be driving the Backend architecture (Node.js) , while occasionally supporting the modern React frontend. If you are passionate about LLMs, prompt engineering, and building robust, scalable systems, this is the project for you. Setup & Work Arrangement Contract: 100% B2 B / Independent Contractor (You must be registered as Autónomo or have a corporate entity in Spain). Location: Hybrid. We require availability to be on-site at our
Requirements
Madrid office 2-3 days per week for architectural alignment, team syncs, and workshops. The rest of the time is remote. Language: Fluent English is required. What You Will Do Take ownership of the backend components, building a sophisticated AI chat platform. Implement new AI provider integrations (Open AI, Claude, etc.) and complex chat functionalities. Design and optimize database structures using Mongo DB and Postgre SQL. Implement and maintain real-time features using Web Socket connections. Ensure code quality through automated testing and participate in high-standard code reviews. Deploy and maintain containerized applications using Docker. Core Technical Stack (Required) Backend (Primary Focus): Node.js (v18+) with Express.js framework. Mongo DB (with Mongoose), Postgre SQL, Redis (for caching & session management). RESTful API design, JWT, and session-based authentication. Frontend: React.js (v18+) with functional components and hooks. Type Script for type-safe development. Tooling & Styling: Vite, Tailwind CSS, Radix UI / Headless UI. State & Data: Tanstack Query (React Query), modern React state patterns, React Router. Dev Ops & Tools: Docker & Docker Compose. Git advanced workflows, ESLint, Prettier. Environment configuration and secrets management. Nice-to-Haves (Bonus Points) Hands-on experience with Open AI API, Anthropic Claude, or similar LLM APIs. Understanding of prompt engineering and AI model integration. Experience with the Lang Chain framework. RAG (Retrieval-Augmented Generation) implementation experience. Why Partner With Us? Work on a modern, open-source AI product. Direct collaboration with product and design stakeholders in a fast-paced, innovative environment. Long-term B2 B collaboration with competitive market rates. #J-18808-Ljbffr ", "employmentType": "FULL_TIME", "industry": "Senior Full", "jobLocation" : { "@type": "Place", "address": { "@type": "PostalAddress", "streetAddress": "Madrid", "addressLocality": "Madrid", "addressRegion": "Madrid", "addressCountry": "ES", "postalCode": "n/a" } }, "salaryCurrency": "EUR", "title": "Senior full stack developer (node.js focus) - open-source ai platform", "hiringOrganization" : { "@type" : "Organization", "name" : "YOPESO Vertriebsgesellschaft MbH" } }