Full Stack Developer, Valencia

Full Stack DeveloperAs PowerUp enters the next stage of our growth, we re now looking to hire an ambitious, motivated Full Stack Developer In this role, you ll work end-to-end across our web and mobile applications, internal telemetry pipelines, and customer-facing intelligence dashboards. You ll collaborate closely with our CTO to build secure, scalable systems that will support rapid growth - and help set the foundation for an engineering team as we expand.PowerUp is building toward an agent-first architecture where AI becomes the primary interface for users. Youll help ensure our applications can surface data to AI agents, support conversational interactions, and integrate with AI services.What you ll do: Design, implement, test, and maintain features end-to-end across frontend, backend, services, and supporting data layers Build and evolve secure, scalable APIs and microservices Ensure robust data flow and integrations between systems, including ingestion and processing pipelines Contribute to architectural decisions with a focus on scalability, security, reliability, and customer experience Implement and improve engineering processes including code reviews, test coverage, documentation, and deployments Help set engineering standards, especially as the team grows Improve and extend existing systems as well as building new features we value developers who read and understand code before rewriting itRequired Proven experience in full-stack development Strong expertise with Next.js, React + TypeScript Familiarity with iOS and Android mobile development (React, Native or similar) Solid backend experience with Node.js, python and/or Ruby Experience working with cloud environments (Azure strongly preferred) Comfortable with fast-paced, ambiguous startup environments where priorities evolve quickly Experience writing unit and integration tests, working with CI/CD, and automating deployments Knowledge of secure coding practices and modern API security approaches Excellent autonomy, ownership, and communication skills in a remote-first team Professional English proficiency (B2+ level)Preferred Experience with Microsoft Data Platform components Experience with the Microsoft Azure App Service or similar cloud web platform. Experience integrating applications with LLM APIs (OpenAI, Claude, Gemini), SLMs or building lightweight agentic workflows. Understanding of how applications feed context to AI agents (RAG patterns, MCP servers, function calling). Understanding of UX principles, ability to work from Figma, and comfort translating user behaviour into intuitive UI Experience scaling systems to handle growth in users, data, or traffic Exposure to NoSQL databases (MongoDB) or experience supporting data migrationsWhy PowerUp Remote-first, flexible working environment. A rare opportunity to join a high-potential start-up and directly influence product, technical direction, and culture. High ownership: your ideas will meaningfully shape the company s trajectory. A team culture that values passion, autonomy, continuous learning, and collaborative problem-solving. A chance to build cutting-edge AI systems with meaningful real-world impact. The opportunity to shape your own career path as our team and product scale.Details: Start date: ASAP Contract Duration: 3 months Contractor/FTE probation period with view to move into FTE Location: Valencia, Spain Competitive salary, with bi-annual salary reviews Annual performance bonus High growth career trajectory Next.js, Java, TypeScript, Python, Node.js, Ruby, Microsoft, Azure, LLMs