Senior Full Stack Engineer - Core UX

This position is listed on behalf of a partner company, who manages all applications and next steps. Our partner is looking for a Senior Full Stack Engineer - Core UX based in Spain.

Join a global engineering team building sophisticated software and AI-powered solutions for a complex, high-impact industry.

As part of the Core UX team, you will refine existing product experiences and ensure the platform feels consistent, responsive, intuitive, and highly polished.

Your work will directly influence how users interact with the product every day, from visual details and interactions to performance and usability.

You will combine strong frontend expertise with full-stack engineering skills to deliver scalable and reliable solutions.

Working alongside full-stack, data, machine learning, and DevOps engineers, you will tackle challenging problems in a highly collaborative environment.

As part of a small, high-performing team, your technical decisions and contributions will have significant influence on both the product and the wider business.

This role is ideal for an experienced engineer who takes ownership, values craftsmanship, experiments continuously, and is motivated by creating exceptional user experiences.

Accountabilities

• Refine and enhance existing product functionality with a strong focus on usability, consistency, responsiveness, performance, and visual quality.
• Improve the overall user experience by paying close attention to layouts, interactions, interface behavior, and product polish.
• Design, develop, debug, and maintain scalable full-stack solutions that support evolving product requirements.
• Contribute to frontend development using modern frameworks, with React experience particularly valuable.
• Develop and maintain backend functionality, including serverless architectures, asynchronous workflows, and cloud-based services.
• Work effectively with relational databases and contribute to reliable, scalable data solutions.
• Collaborate closely with full-stack, data, machine learning, and DevOps engineers across a globally distributed team.
• Take end-to-end ownership of projects, driving initiatives from initial problem definition through implementation and completion with minimal oversight.
• Proactively communicate progress, surface blockers, ask thoughtful questions, and keep relevant stakeholders informed.
• Experiment with new approaches, measure results, and iterate rapidly to solve complex or previously unsolved technical and product challenges.
• Contribute to a culture centered on high standards, customer impact, transparency, accountability, continuous experimentation, and technical excellence.

Requirements

• 5+ years of professional software engineering experience, ideally including a strong track record of improving and polishing product functionality to deliver a premium user experience.
• Strong software engineering fundamentals, including system design, debugging, architecture, and structured problem-solving.
• Professional experience with a modern frontend framework, preferably React.
• Strong knowledge of JavaScript, TypeScript, and/or Python; candidates with equivalent experience in other object-oriented programming languages are also encouraged to apply.
• Experience with serverless technologies and cloud environments, including platforms or services such as AWS Lambda and EC2.
• Experience designing or working with asynchronous workflows and scalable backend systems.
• Solid experience with relational databases, ideally PostgreSQL.
• Strong attention to detail and a genuine appreciation for high-quality, polished user experiences.
• Demonstrated ownership, initiative, resilience, and the ability to drive projects forward with limited supervision.
• Excellent communication skills and a proactive approach to collaboration in a distributed, cross-functional environment.
• Comfortable experimenting, measuring outcomes, learning quickly, and iterating on challenging problems.
• Experience with LLMs, generative AI, or distributed systems is a valuable advantage.
• Ability to thrive in a fast-paced growth environment with ambitious goals and a high degree of responsibility.
• Authorization to work in the European country where you are based; the role is offered through a B2B or contractor arrangement, and visa sponsorship is not available.

Benefits

• Competitive salary ranging from $80,000 to $165,000 USD, depending on experience, performance, and geographic location.
• Significant equity options package.
• 20 days of paid time off per year.
• Global team offsites and opportunities to connect with colleagues internationally.
• Phone reimbursement.
• Gym reimbursement.
• Student stipend.
• Opportunity to work alongside ambitious, highly skilled professionals across engineering, data, machine learning, and DevOps.
• Significant individual impact within a small, high-performing team.
• Opportunity to work on challenging technology and AI problems while helping transform a major global industry.
• An environment that emphasizes ownership, experimentation, transparency, continuous learning, and measurable customer impact.