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Senior Full Stack Developer (Node.js Focus) – Open-Source AI Platform

YopesoMadrid, Comunidad de Madrid, Spain
Hybrid Contract

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Experience Level

Senior

Qualifications

RequirementsAbout the ProjectWe are developing an advanced, open-source AI conversational platform that integrates various AI providers to provide a rich, state-of-the-art user experience. We seek a seasoned Senior Full Stack Developer to become an integral part of our core team as a B2B partner. This role is primarily full-stack, with approximately 80% of your responsibilities centered on enhancing the Backend architecture (Node.js), while occasionally contributing to the modern React frontend. If you have a passion for LLMs, prompt engineering, and building robust, scalable systems, this project is tailor-made for you. Setup & Work ArrangementContract: 100% B2B / Independent Contractor (must be registered as an Autónomo or have a corporate entity in Spain). Location: Hybrid. We require your presence at our Madrid office 2-3 days per week for architectural alignment, team syncs, and workshops. The remainder of the time can be remote. Language: Fluent English is a must. What You Will DoTake charge of backend components to construct a sophisticated AI chat platform. Integrate new AI providers (such as OpenAI, Claude, etc.) and develop complex chat functionalities. Design and optimize database structures using MongoDB and PostgreSQL. Implement and maintain real-time features utilizing WebSocket connections. Ensure code quality through automated testing and engage in meticulous code reviews. Deploy and maintain containerized applications.

About the job

Yopeso brings nearly two decades of experience in software development, building both large-scale systems and tailored products. The company employs more than 300 professionals across five global locations, with a steady focus on growth, transparency, and professionalism throughout each project.

Authenticity, curiosity, and ambition shape daily work at Yopeso. Teams operate with trust and integrity, maintaining open communication and a commitment to secure, reliable software. Each project emphasizes high quality and dependable performance.

Collaboration plays a central role. Agile teams share knowledge and support one another, working efficiently to deliver software that aligns with the company’s core values and meets real-world needs.

About Yopeso

Yopeso is a leading software development company with 20 years of experience, specializing in diverse software products, including large-scale applications and tailored solutions. We prioritize a culture of growth, transparency, and professionalism, with a dedicated team across multiple locations.

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