Principal UI Engineer - Design/Developer Tools

Yahoo serves as a trusted guide for hundreds of millions of people globally, helping them achieve their goals online through our portfolio of iconic products. For advertisers, Yahoo Advertising offers omnichannel solutions and powerful data to engage with our brands and deliver results. A Little About Us Yahoo is a global media and tech company that connects hundreds of millions of people to the things they love, from finance and sports to news and entertainment. Our engineering teams build high-performance, accessible, and resilient digital experiences at scale. Our team builds the core platform, collaborative canvas, and design-to-code infrastructure that engineers and designers across Yahoo use to create and ship product UI. We care about runtime latency, distributed consistency, and fast, reliable developer workflows. We work where modern frontend architecture, real-time collaboration, and AI-augmented developer tooling meet, and we aim to raise the engineering bar across the organization. A Lot About You You're a seasoned Principal Engineer who cares deeply about how complex systems behave under load, under failure, and during high-concurrency collaboration. You're fluent across the entire surface: you can profile a React render tree and an AST transform pipeline in the morning, and trace a dropped CRDT sync through a WebSocket server, Redis, and Postgres in the afternoon. You still enjoy building UI, but most of your energy goes into making the platform beneath it fast, durable, observable, and safe to change. You think in invariants: no user edit is ever silently lost, every deploy can be safely rolled back, and regressions are caught in CI before they reach production. You treat AI tools as collaborators and as building blocks in your systems, not just as typing accelerators. You take pride in mentoring senior engineers, communicating clearly with cross-functional partners, and continually evolving how the team works. Responsibilities Platform Architecture & Core Infrastructure: Own the architecture, scalability, and uptime of our real-time collaboration server, Postgres-backed persistence layer, background jobs, and the APIs that sit on top of them. Collaborative Systems & Data Integrity: Design, harden, and evolve multi-user editing built on CRDTs (Yjs). Guarantee reliable sync, reconnection, conflict handling, undo/redo, and save durability, so users' work is never silently lost across disconnects, deploys, or branch switches. AI-Augmented Developer Tooling & Agent Interfaces: Architect and maintain agent-ready interfaces, Model Context Protocol (MCP) servers, and automated pipelines that let AI coding agents and developers safely inspect, generate, and change design systems and codebases. Performance & Canvas Engineering: Profile and optimize end-to-end bottlenecks: interactive canvas rendering, frame rates, hydration and bundle payloads, query cost, memory footprint, and server event-loop health. Build performance benchmarks and enforce regression budgets in CI. Developer Infrastructure & Monorepo Operations: Steer the evolution of our large TypeScript monorepo, CI/CD pipelines, automated testing, and preview, staging, and production environments so shipping stays fast, reproducible, and safe. Observability & Systemic Resilience: Define SLOs, metrics, structured logging, and real-time alerting. Champion incident management, lead blameless post-incident reviews, and turn root causes into durable, platform-level fixes. Security & Access Control: Partner on authentication, authorization, and permission models across systems, branches, and files, so access rules are enforced consistently everywhere. UI Engineering: Contribute to product UI in React and TypeScript, especially where performance, state management, and data flow matter most. AI Workflow Leadership & Quality: Set standards for using AI coding agents across the software lifecycle, backed by rigorous review, static analysis, and testing that validate AI-assisted output for accuracy, security, and maintainability. Technical Mentorship & Governance: Set engineering standards for reliability, code hygiene, and accessibility. Mentor staff and senior engineers, lead high-impact architecture reviews, and align engineering, product, and design roadmaps. Qualifications 8+ years of experience designing, building, and operating production-scale web platforms, with significant time on both front-end and back-end/platform work. Advanced mastery of modern TypeScript, JavaScript, React, and server-side runtimes (Node.js or Bun). Hands-on experience with real-time data models, WebSockets, and collaborative editing (CRDTs such as Yjs or Automerge, or OT), with a solid grasp of consistency, concurrency, and failure modes. Strong SQL and relational database (PostgreSQL) foundations, including schema evolution and access-control patterns. A track record of diagnosing and resolving complex performance issues in the browser (rendering, Web Vitals, memory) and on the server (latency, throughput, resource usage), using profilers, heap snapshots, and tracing. Experience running production services: metrics, alerting, structured logging, on-call, and designing for graceful degradation. Experience with cloud and serverless deployment platforms, containerized services, CI pipelines, and multiple environments (preview, staging, production). Daily, productive use of AI coding agents and LLM-based CLI tooling for code generation, refactoring, and test authoring. Clear technical communication and proven leadership in driving architectural consensus across engineering, design systems, and product stakeholders. Preferred Qualifications Experience building, evaluating, or operating LLM-backed features, agentic developer tooling (tool calling, streaming), or Model Context Protocol (MCP) servers. Expertise with large monorepo build orchestration (Turborepo, Nx) and code generation tooling (Babel/SWC plugins, AST manipulation). Hands-on familiarity with Supabase or managed Postgres, row-level security, migrations at scale, and Redis caching layers. Experience building comprehensive automated test suites across unit, integration, and end-to-end frameworks (Playwright, Bun test, Jest) tied to CI performance gates. Familiarity with design system tokens, component libraries, and design-to-code pipelines. This isn't required, but it helps. The material job duties and responsibilities of this role include those listed above as well as adhering to Yahoo policies ; exercising sound judgment ; working effectively, safely and inclusively with others ; exhibiting trustworthiness and meeting expectations ; and safeguarding business operations and brand integrity. At Yahoo, we offer flexible hybrid work options that our employees love! While most roles don't require regular office attendance, you may occasionally be asked to attend in-person events or team sessions. You'll always get notice to make arrangements. Yahoo is proud to be an equal opportunity workplace. All qualified applicants will receive consideration for employment without regard to, and will not be discriminated against based on age, race, gender, color, religion, national origin, sexual orientation, gender identity, veteran status, disability or any other protected category. Yahoo will consider for employment qualified applicants with criminal histories in a manner consistent with applicable law. Yahoo is dedicated to providing an accessible environment for all candidates during the application process and for employees during their employment. If you need accessibility assistance and/or a reasonable accommodation due to a disability, please submit a request via the Accommodation Request Form ( ) or call View phone number on click.appcast.io . Requests and calls received for non-disability related issues, such as following up on an application, will not receive a response. We believe that a diverse and inclusive workplace strengthens Yahoo and deepens our relationships. When you support everyone to be their best selves, they spark discovery, innovation and creativity. Among other efforts, our 11 employee resource groups (ERGs) enhance a culture of belonging with programs, events and fellowship that help educate, support and create a workplace where all feel welcome. The compensation for this position ranges from $143,625.00 - $299,375.00/yr and will vary depending on factors such as your location, skills and experience.The compensation package may also include incentive compensation opportunities in the form of discretionary annual bonus or commissions. Our comprehensive benefits include healthcare, a great 401k, backup childcare, education stipends and much (much) more. #J-18808-Ljbffr Yahoo Holdings Inc.