Senior Backend Engineer (Foundation)

Proton, the privacy‑first company founded by CERN scientists in 2014, delivers encrypted services such as Proton Mail, VPN, Drive, Pass and Calendar to millions worldwide. The Senior Backend Engineer will join the Foundation team, which creates the shared backend framework, internal libraries and common services that underpin every Proton product. In this role you will design and implement reusable libraries, framework layers and internal services, turning repeated patterns into clean abstractions. You will produce documentation and examples that encourage adoption, and you will enhance the developer experience by improving build times, local development setups, test ergonomics and debuggability. Collaboration is central: you will engage with product teams through RFCs, design reviews and occasional pull requests, and you will work closely with other engineers to integrate your libraries smoothly into their applications. The position requires at least five years of experience building and operating production backend systems, with a strong focus on modern PHP. You must have a working knowledge of Rust—or be able to acquire it quickly—and demonstrate a solid sense of API design, including naming, defaults, error handling and the distinction between libraries and services. Experience shaping architecture at scale, maintaining healthy monorepo boundaries, evolving shared code without breaking downstream teams, and thinking about security implications are essential. You also need the influence to drive adoption of internal libraries and the patience to resolve disagreements between teams. Additional strengths that are valued include familiarity with Domain‑Driven Design, developer‑tooling or platform work, contributions to open‑source libraries, incremental code‑base migrations, applied cryptography or key‑management expertise, and experience building CI/CD pipelines. Proton’s team spans more than 500 people in over 50 countries, operates profitably without venture‑capital control, and selects only the top fraction of applicants, offering a fast‑moving environment where impact is prized over hierarchy.