Senior Fullstack Engineer (Freelance)

Senior Fullstack Engineer (Freelance) Want to use your energy and talent to tip the balance on climate change? We're looking for a Senior Fullstack Engineer to work on our Sustainability Data Intelligence Platform. Sweep is looking for a Senior Fullstack Engineer (freelance) to work on our Sustainability Data Intelligence Platform. Climate change is the defining issue of our time. Sweep builds a sustainability data intelligence platform used by major enterprises to track greenhouse gas emissions, meet regulatory requirements, and drive real decarbonization. We're a B Corporation, and we mean it. Ok, sounds promising. What will I be doing? As a Senior Fullstack Engineer, you'll own features end-to-end, from data models and backend systems to the interfaces that make sustainability data actionable. You'll work at the heart of our core product, alongside a team that cares deeply about quality and impact. What you'll be working on: Build and own core product features - Design and implement full-stack features from the ground up: database schema, backend logic, GraphQL API, and React/TypeScript UI - Take full ownership of significant parts of the system: reliability, performance, and long-term maintainability are yours to drive - Participate in every stage of the development lifecycle, from design and implementation to rollout and smooth operation in production - Contribute to and challenge our technical architecture as we scale Bring genuine backend depth - Design robust data models and schemas built to perform at scale - Build and operate backend services, including background jobs, async pipelines, and integrations with third-party systems - Own observability: instrument systems, define meaningful metrics, and respond to incidents with confidence - Identify and address security risks proactively from API design to infrastructure exposure - Automate deployments via our CI/CD systems and continuously improve development processes Work with AI as a day-to-day accelerator - Leverage AI tools actively in your workflow, from code generation and review to debugging and documentation, to move faster without compromising quality - Contribute to how we integrate AI-assisted development practices across the engineering team - Stay curious about emerging AI capabilities and bring new ideas on how we can use them to ship better, faster Be a team force multiplier - Lead technical design on significant features and share your experience openly - Review pull requests with rigour and care, raising the bar for the whole team - Participate actively in team rituals: stand-ups, planning, retros - Contribute to our culture of quality: incremental, well-tested, observable changes Pursue quality, always - Champion clean code, solid test coverage, and strong engineering practices - Improve processes and methodologies to reach the highest standards - Bring excellence to your own work and help others do the same That sounds just right for me. What do I need to bring? Glad you asked. This is who we’re looking for: 5+ years of experience shipping product across the full stack, with strong backend foundations Solid experience with Ruby on Rails in a high-scale production environment is a must Fluent in React/TypeScript on the frontend; deep expertise in relational databases, distributed systems, observability, and security on the backend Comfortable owning features end-to-end with autonomy and clear communication You write clean, well-tested code and take genuine ownership of your work Practical Details Hybrid or Remote. Offices in Paris, London, Montpellier, and Denver Start date: ASAP Duration: Long-term collaboration, renewable Rate: 520€ Department Engineering Role Fullstack Engineer Locations Paris, Montpellier, London Remote status Fully Remote Daily salary €500 Employment type Contract About SWEEP Sweep is a sustainability data management platform. Though our primary focus is on environmental action, Sweep supports clients with all ESG goals, including waste reduction, water usage, biodiversity impacts, social equity and transparency in governance. We’re building a business that’s good for everyone, including society and the planet. That’s why we have B-Corp status and are an entreprise à mission, with our own committee that helps us keep to our manifesto . We’re committed to building an inclusive company, with a diverse group of talented people who all feel valued, feel like themselves, and thrive. Founded in 2020