Who you are
- 5+ years building and operating backend systems in production, including code you stayed responsible for long after launch, with a focus on modern PHP
- Working knowledge of Rust, or clear evidence you can get there quickly — we care that you understand ownership and lifetimes
- Genuine taste in API design. You have opinions about naming, defaults, error handling, and what belongs in a library versus a service
- A feel for architecture at codebase scale — you have worked somewhere large enough that module boundaries and dependency direction mattered, and you have views on what keeps a monorepo healthy
- Experience evolving shared code that other teams depend on, and doing it without breaking them
- A security mindset. You think about how the abstraction you just wrote will be misused
- The influence to get an internal library adopted rather than worked around, and the patience to carry a design through disagreement between two teams who both think they're right
- Domain-Driven Design, or similar experience modelling complex domains where the boundaries matter




- Background in developer tooling, platform, or DX teams
- Contributions to open source, especially libraries with real users
- Experience migrating a codebase incrementally between architectures or languages
- Experience with applied cryptography, key management, or end-to-end encrypted systems
- Experience with building CI/CD
- Even if you don’t meet all the requirements listed above, but feel you could still be a great fit, please still apply
What the job involves
- The Foundation team builds what the product teams build on: the shared backend framework, the internal libraries, the common services and abstractions that every Proton application reaches for. If several teams need it, it should exist once, and be good
- You will work in PHP for API related work, and in Rust for components where performance and memory safety justify it or for microservices. You will own libraries or initiatives end

📌 Senior Backend Engineer (Barcelona)
🏢 Proton
📍 Barcelona