Senior Full Stack Engineer (React & Java) in Madrid or Remote

About the Position

Senior Full Stack Engineer (React & Java) in Madrid or Remote

We are looking for a Senior Full Stack Engineer with a strong focus on modern web frontend and hands-on experience building backend services to join our e-commerce SaaS team at Treatwell. You will be responsible for taking ownership of features across the stack, from database schema and backend services to the UI, from design through deployment and operations.

Responsibilities

• Take ownership of features across the stack, from database schema and backend services to the UI, from design through deployment and operations.
• Pair with engineers, designers, and PMs to ship features every cycle, iterating based on real usage and feedback.
• Participate in design and code discussions, making trade-offs and decisions that affect the product and the team.
• Maintain a strong focus on automated testing, applying the testing pyramid to ensure unit, integration, and end-to-end coverage.
• Improve observability across services and the frontend by adding metrics, dashboards, and alerts with tools like Datadog, Sentry, and web vitals.
• Design and build backend services and APIs in Java and Spring Boot, including event-driven flows with RabbitMQ.
• Own your services end-to-end, with a DevOps mindset, from architecture through deployment and operations.
• Validate ideas with data: instrument your work, measure its impact, and use evidence to decide what to scale.
• Be an active part of the Engineering Guild, collaborating with other engineers to share ideas, improve standards, and tackle cross-team challenges.
• Lead technical discussions about trade-offs in features, architecture, and UX, helping the team make informed decisions that balance product goals and engineering constraints.
• Navigate a hybrid codebase, balancing work between legacy systems and modern React/TypeScript.
• Build internal tools that help operations and support teams move fast without creating risk.

Requirements

• 7+ years of software development experience, with a strong focus on modern web frontend and hands-on experience building backend services.
• You take responsibility for the code you write and the areas you own, spotting bugs, performance issues, or UX gaps, and fixing them proactively without waiting for direction.
• You own features end-to-end, from database schema to UI, without needing a handoff.
• You have a product mindset. You think about the person using what you build, ask why before how, and push back when something doesn't make sense.
• You think in systems and trade-offs, and you look for the upstream cause, not just the downstream symptom.
• You are data-driven. You instrument your work, measure impact, and use evidence to make decisions.
• You actively leverage AI tools in your daily development workflow, viewing them as force multipliers for productivity, code quality, and problem-solving.
• You are comfortable with ambiguity in complex domains and can make progress without getting paralysed.
• You have sharp product thinking and a focus on UX, paying attention to the little things: edge cases, empty states, and error handling.
• You have excellent English communication skills and can explain complex technical ideas clearly to engineers, designers, and non-technical stakeholders.
• You are comfortable working with remote and co-located teams, and you are structured, analytical, and highly collaborative.

Our Stack

Frontend: React, TypeScript, React Query, Storybook, Jest, Cypress

Backend: Java, Spring Boot, RabbitMQ, PostgreSQL, MS-SQL

Infrastructure: Kubernetes, GitLab CI/CD, AWS, Datadog

Mindset: DevOps, DDD, event-driven architecture

We Offer

• 28-days holiday, plus bank holidays
• Monthly €40 Treatwell vouchers so you can treat yourself too
• Mental health support through our partnership with Open-Up
• Market-specific benefits that will be discussed in the interview process

About the Company

Treatwell is an 'Open to All' employer and warmly welcomes everybody to the team. We are committed to making reasonable adjustments to the recruitment process as required. Please add any adjustment requests to your application.

Website: https://www.treatwell.com

Industry: E Commerce

Headquarters: London, UK

Company Size: 500 - 1,000

Founded: 2008