Senior Full Stack Engineer - AI Harness

The role / impact This senior engineering position owns a critical delivery stream on MyXero, the foundational platform that underpins every organisation and user record while managing hundreds of millions of daily requests. You will take ambiguous platform challenges from problem framing to durable architectural solutions, designing the specs, verification harnesses, and AI guardrails that enable software agents to handle implementation safely. Your work directly enables the modernisation of a massive system into decoupled domain services without disrupting dependent products. By engineering automated verification loops and robust testing harnesses, you will ensure high reliability, mentor team members, and shape how our engineering practices operate safely with intelligent tools. The team / how they connect You will join the MyXero Ghostbusters squad within our Identity and Platform group, collaborating with engineers and product partners primarily based across New Zealand. The team operates with a written-first, remote-first philosophy, using design records, paired kick-offs, and blameless reviews to ensure every voice is heard and no one works in isolation. While delivery is high-tempo, the group maintains a supportive, open environment where technical curiosity and shared learning are core to daily routines. Initially, you will focus on - Setting up an intentional local development harness with automated validation checks to safely handle production changes. - Refactoring legacy monolith endpoints and services built on .NET Framework, C#, and SQL Server towards modern APIs. - Developing automated verification loops, test simulation harnesses, and tools that reduce operational toil and human checks. - Building cloud agent tooling and collaborative workflows that support the evolution toward an automated development lifecycle. Where and how you can work This role is open to candidates based in New Zealand, offering a flexible remote-first setup with office access in Wellington or Auckland. Our working environment is structured around async communication and balanced collaboration. Here are some of the things we are looking for - You bring deep full-stack or backend engineering experience with typed languages, ideally with exposure to C# and .NET environments. - Hands-on exploration with AI harnesses, coding agents, or automated verification pipelines in a personal or professional setting. - Practical familiarity with distributed systems architecture, API design, data modeling, and managing complex relational database migrations. - Proven capability in taking ambiguous technical problems from initial conception to production delivery. - Strong written communication skills to articulate system trade-offs clearly through design records and technical documentation. - A collaborative mindset with a drive to share learnings, uplift team capabilities, and contribute constructively to production support rotations. Apply even if your experience isn't a perfect match! At Xero, we hire based on your skills, passion, and the unique perspective you can bring to enhance our culture and team.