Senior Frontend Engineer - AI Platform

We are currently seeking a Senior Frontend Software Engineer to join the AI Platform team, Addepar's next-generation AI platform that enables seamless insights and interaction through natural language and data intelligence across our AI products.

As a Senior Frontend Engineer, you'll design and scale the interactive surface of AI platform products. You'll work at the intersection of AI, design, and systems engineering, building a class of real-time AI experiences for users where every frame, token, and scroll behaviour matters. You will collaborate closely with product design, backend, and AI/ML engineers to deliver smooth, trustworthy AI experiences that align with Addepar's standards of performance, transparency, and reliability. Applicants must have legal authorisation to work in the country where this role is based on the first day of employment. Visa sponsorship is not available for this position.

Responsibilities:

• Design and implement complex, real-time UI features for conversational interfaces, including chat streaming, incremental rendering, and dynamic layouts.
• Build high-performance WebSocket pipelines to handle streamed deltas, retries, and backpressure gracefully.
• Optimise scrolling and rendering performance using requestAnimationFrame, virtualisation, intersection observers, and non-blocking state updates.
• Implement fault-tolerant UI logic for reconnection, cancellation, offline recovery, and retry without user disruption.
• Architect state management and caching strategies to maintain consistency between local UI and backend deltas.
• Collaborate with designers to deliver accessible, responsive, and pixel-perfect interfaces across themes and viewport sizes.
• Extend Addepar's frontend developer experience: refine the build pipeline (Vite/Webpack), test automation (Playwright, Jest), and linting/formatting standards (ESLint, Prettier).
• Instrument client-side telemetry and performance metrics to measure render latency, streaming lag, and user interaction speed.
• Mentor teammates through design reviews and pair programming, contributing to shared components and cross-product standards.
• Work closely with backend and AI/ML teams to co-design message formats, token streaming APIs, and session-level resiliency mechanisms.
• Shape the technical direction of the AI platform's frontend, contributing to shared libraries and caching strategies.

Requirements:

• Bachelor's degree in computer science, engineering, or a related technical field (or equivalent practical experience).
• At least 5 years of professional frontend development experience in a production environment.
• Strong proficiency in TypeScript/JavaScript and deep understanding of asynchronous browser behaviour.
• Experience with Svelte, React, or another component-based modern UI framework.
• Strong debugging and performance profiling skills.
• Experience integrating real-time or streaming data into user interfaces.
• Strong communication, collaboration, and mentoring skills.
• Additional certifications or licenses
• Skills and competencies that also include soft skills necessary for success
• Bonus: Familiarity with AI/LLM-powered interfaces, progressive streaming UIs, or data-rich visualisation frameworks.
• You care deeply about user experience, developer productivity, and measurable performance, and you know that excellence in frontend engineering is achieved through curiosity, rigour, and empathy for both users and teammates.

Browser and Rendering Fundamentals:

• Deep understanding of the browser's rendering pipeline: DOM, CSSOM, layout, paint, and compositing.
• Ability to identify and fix layout thrashing, paint storms, and jank through Chrome DevTools performance profiling.
• Knowledge of animation scheduling via requestAnimationFrame, idle callbacks, and microtask queues. Familiarity with modern web APIs such as IntersectionObserver, ResizeObserver, MutationObserver, OffscreenCanvas, Web Workers, and BroadcastChannel for concurrent or cross-tab coordination.

Asynchronous and Streaming Systems:

• Strong command of Promises, async/await, generators, and cancellation (AbortController).
• Familiarity with streaming data protocols (e. g., WebSockets and SSE) and patterns like batching, throttling, and debouncing under load.
• Understanding of backpressure and how to pace UI rendering vs. message ingress.

State and Data Synchronisation:

• Experience designing immutable data flows with fine-grained updates (diffs, patches, deltas).
• Knowledge of caching, reconciliation, and hash-based change detection (e. g., djb2 and CRC32 content hashing).
• Practices for ensuring consistency between transient client state and authoritative backend models.

UI Architecture and Composition:

• Familiarity with reactive component frameworks (Svelte preferred; React/Vue acceptable).
• Experience isolating side effects, using stores/signals, and maintaining predictable reactivity graphs.
• Ability to decompose large applications into feature modules with lazy loading, error boundaries, and shared design tokens.
• Ability to evaluate and integrate across frameworks (Svelte, React, and Web Components) while maintaining consistent patterns in state, testing, and accessibility.

Performance and Profiling:

• Proven skill in measuring and optimising UI latency (first paint, input delay, FPS stability).
• Comfort with Chrome Performance, Lighthouse, or custom performance markers. Experience building virtualised views (infinite scroll, chat lists, large tables).

Design Systems and Accessibility:

• Experience building and maintaining reusable design systems with Storybook, Tailwind, or Web Components. Knowledge of accessibility standards (WCAG, ARIA) and best practices for keyboard, colour, and screen reader support. Skilled at collaborating with design teams to translate high-fidelity Figma designs into performant, production-ready components.

Resilience, Testing and Observability:

• Writes defensive code to handle partial data, dropped connections, race conditions, and AbortErrors.
• Understands test pyramids: unit, integration, and end-to-end (Playwright, Jest, Vitest).
• Adds telemetry hooks and log events to diagnose production issues and user experience regressions.

Developer Experience and Tooling:

• Comfortable configuring bundlers (Vite, Webpack) and optimising build times.
• Sets up linting, type checking, and pre-commit automation for consistency.
• Experience with CI/CD, incremental testing, and feature flag rollouts.
• Experience with AI-assisted developer tools or scripting build/test automation to improve team velocity.

Mindset:

• You think in systems, not pages.
• You balance aesthetics with performance, correctness, and maintainability. You obsess over the invisible details - micro-interactions, latency, and flow - that make complex products feel effortless.
• You enjoy teaching others, debugging difficult issues, and making the team move faster through better abstractions.