Rein is looking for a Senior Software Engineer

Rein was founded with one simple mission: to uncover the reality of how applications behave in production.

We build a new technology that lets application security and agentic AI teams see risk as it really is. The result: faster, smarter security decisions based on what’s truly happening inside your apps.

Backed by Glilot Capital, Rein is already trusted by leading companies across banking, energy, and SaaS.

We’re looking for people who love solving big challenges quickly and creatively. Builders who enjoy turning rough ideas into real products, aren’t afraid of hard problems, and thrive in the pace and ambiguity of an early-stage startup. People who are comfortable being technologically versatile, jumping across problems and stacks when needed, and who care about seeing their work make a real impact on customers. Most of all, teammates who push themselves, support each other, and enjoy building something meaningful together.

What You’ll Do

• Solve complex, high-impact problems that require a deep understanding of runtime and os internals.
• Write highly efficient production-grade code, primarily in C++, and also in other languages such as Python, Node.js, Java, and more.
• Be part of a small, fast-moving team where you’ll have real ownership and influence, and the opportunity to push forward ideas and practices that matter to you.
• Design and build robust internal infrastructure that enables rapid execution without compromising quality.

Required Skills

• 5+ years of professional, hands-on C++ experience, building and maintaining complex systems
• Proven experience developing production-grade software, with strong emphasis on correctness, reliability, performance, and maintainability
• Solid understanding of Linux or Windows OS Internals
• Excellent problem-solving and debugging skills
• Able to rapidly implement, verify ideas, and translate them into efficient and reliable operational code
• Solid testing discipline: writing and maintaining unit, integration, and end-to-end tests
• Ability to quickly onboard into an existing codebase, understand its architecture, data flows, and system behavior, and contribute effectively
• Experience with various runtime environments (python, nodejs, java) - Bonus