Full Stack Developer, Valencia

Full Stack Developer
As 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 it

Required
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 migrations

Why 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