Senior Fullstack Engineer (Freelance)

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.

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:

1. 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
   

2. 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
   

3. 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
   

4. 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
   

5. 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

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

• Hybrid or Remote. Offices in Paris, London, Montpellier, and Denver

• Start date: ASAP

• Duration: Long-term collaboration, renewable

• Rate: 520€