Senior Front End Engineer

Senior Frontend EngineerCardiovascular care is often the #1 cost for health plans and employers, with the current fee for service model incentivizing providers to maximize volume and throughput at the expense of clinical outcomes and patient satisfaction. Karoo's mission is to improve the lives of every cardiac patient in America by transforming the current care model to improve patient outcomes at significantly lower cost. Karoo deploys a value-based approach which combines a blend of traditional, guideline-based medicine and state of the art digital tools to accomplish this important mission by enabling the conversion to, and success in, value-based care arrangements for cardiovascular networks, health systems and payers. Karoo is backed by leading venture capitalists, including First Trust Capital Partners and BIP Ventures, and has near and medium-term plans for further rounds.About the RoleWe are looking for a hands-on Senior Frontend Engineer to own our frontend architecture and user experience. You will design, build, and maintain our complex web applications from the ground up while working closely with product and backend teams. This role requires high technical autonomy, deep production discipline, and a strong sense of ownership.What You'll DoArchitect State & Data Fetching: Build custom client-side state architectures and raw data-fetching systems (fetch, AbortController, signal composition, request deduplication, cache freshness, and structured error envelopes with correlation IDs) without relying on heavy external state libraries.Maintain High-Fidelity UI & Design Systems: Author and maintain production design-system primitives using React 18 and utility-first Tailwind CSS.Deliver Complex Clinical Workflows: Build multi-section clinical forms with field-level validation, partial-save/dirty-state handling, server-side error mapping, and strict date/timezone handling (TZ=America/New_York).Enforce Strict Quality & Accessibility: Write accessible UI patterns (focus trapping, keyboard navigation, aria-invalid, dynamic live regions) and maintain high test coverage using Vitest and React Testing Library.Protect Patient Privacy (HIPAA/PHI): Maintain strict client-side PHI guards, keeping logs, analytics, and third-party tools completely free of sensitive patient data.Cross-Stack Collaboration: Trace API contracts directly into backend source code (Python/FastAPI) and implement router-level authorization models with feature flags. Architect, develop, and maintain modern, scalable web applicationsQualificationsReact 18 & State Architecture: Deep mastery of React hooks discipline, context composition, dynamic imports (lazy/Suspense), and building custom client-side state solutions without Redux, Zustand, or React Query.Advanced TypeScript: Expert knowledge of generics, discriminated unions, unknown-first API parsing, and strict type-safety.Custom Fetching Engine: Direct experience managing client-side request lifetimes, signal cancellation, timeouts, caching, and custom error boundaries.Production Accessibility: Practical implementation of complex ARIA patterns, live regions (role="alert"/status), focus-trap management, and keyboard navigation.Automated Testing Discipline: Extensive experience with Vitest, jsdom, and React Testing Library, testing by accessible roles rather than internal implementation details.Tailwind & Design Systems: Experience building primitive UI libraries with stable prop APIs using Tailwind CSS and design-token systems.Date & Timezone Correctness: Strong understanding of IANA timezones, local vs. UTC offsets, DST, and bare business dates.Browser Profiling & Monorepo Workflows: Skill in diagnosing re-render bottlenecks, devtool network traces, Git MR workflows, and reading Python/FastAPI backend contracts.PHI/HIPAA Safeguards: Strict awareness of data privacy constraints on the client side.Nice to HavesTesting and Tools: Playwright end-to-end testing, OpenAPI client codegen, and automated accessibility testing (axe/jest-axe).Domain & UI Patterns: Healthcare domain knowledge (cardiology/GDMT, FHIR, care management), complex calendar/scheduling UIs, list virtualization, or WebRTC/Twilio Voice SDK integrations.Infrastructure & Build: Vite/bundler tuning, Docker Compose monorepo setups, and SPA delivery (S3, CloudFront, CSP, light Terraform).Ecosystem Trends: Familiarity with headless components (Radix, HeadlessUI) and React 19 /Server Components.