Principal Software Engineer - AI Foundations

Toast creates technology to help restaurants and local businesses succeed in a digital world, helping business owners operate, increase sales, engage customers, and keep employees happy. Because our technology is purpose-built for restaurants, by restaurant people - and increasingly shaped by AI in both what we build and how we build - restaurants can trust that we'll deliver on their needs for today while investing in the experiences that will power their restaurant of the future. AI Foundations is Toast's internal platform team for AI. We build the infrastructure, governance, and developer tooling that makes AI a reliable, scalable force multiplier across the entire product development lifecycle. Our products include the LLM Proxy, AI Key Management, Observability pipelines, the Claude Plugin Marketplace, and autonomous agents that participate directly in the software development lifecycle. As a Principal Software Engineer, you'll set the technical direction for how we design, build, and evolve these systems, working full-stack across the agentic workflows that employees across Toast depend on every day. This role is for someone who can drive architecture, raise the engineering bar across the team, and stay hands-on building. A day in the life (Responsibilities) Define and drive the technical architecture for AI Foundations platform, spanning backend services, frontend tooling, and third party integrations Lead full-stack design and delivery across the LLM proxy, AI key management, observability pipelines, and internal plugin marketplace Architect and deliver autonomous agents and MCP services that participate in the software development lifecycle Set and uphold engineering standards across the team: code quality, system design, testing, and operational practices Mentor and technically lead engineers across all levels through design reviews, code reviews, and pairing Partner with product and platform leadership to shape the AI Foundations roadmap and translate strategy into executable technical plans Collaborate closely with designers and product teams to translate UX concepts into polished, production-ready frontend experiences Serve as a key technical voice in cross-team discussions, representing AI Foundations in architecture decisions across Toast engineering What you'll need to thrive (Requirements) 10+ years of experience designing and delivering scalable software systems, with a strong full-stack background spanning backend services and frontend or developer-facing interfaces Demonstrated experience leading technical architecture for a platform, product, or engineering team Proven ability to mentor engineers and raise the technical bar of a team through standards, reviews, and hands-on guidance Experience building, deploying, or operating LLM-powered agents or AI platform infrastructure Familiarity with AI coding assistants (e.g., Claude Code, Cursor, GitHub Copilot) and experience extending them through custom plugins, skills, or hooks Experience with MCP, tool use patterns, or agentic frameworks Strong foundation in modern backend (Java, Kotlin, or similar) and frontend (TypeScript, React, or similar) technologies, with demonstrated experience building user-facing product interfaces Comfort with a rapidly changing technical landscape and a bias towards action over analysis paralysis What will make you stand out Familiarity with A2A (Agent-to-Agent) protocols and multi-agent orchestration patterns Experience with machine learning concepts, model evaluation, or ML infrastructure Experience building developer experience platforms or internal tooling Familiarity with observability tooling for AI/LLM systems (e.g., Langfuse, DataDog) **This role requires a minimum of two days per week in our Dublin office** AI at Toast At Toast, one of our company values is that we're hungry to build and learn. We believe learning new AI tools empowers us to build for our customers faster, more independently, and with higher quality. We