Yaroslav Sergievskiy
Software Engineer / Staff Engineer
I am a UI engineer with 12+ years of experience and an expert at building for the Web. I specialize in developing long-living maintainable apps with fast and polished User Interfaces, while taking end-to-end ownership of the systems behind them.
It's my responsibility to follow the Web Platform best practices in order to deliver semantically correct, accessible, and fully keyboard-navigable Web Applications. Beyond the UI layer, I regularly design and implement backend APIs and services that power web and mobile clients, and work closely with product and platform teams to ensure scalability, performance, and clean integration boundaries.
While I develop mostly in React, I actively follow and form opinions on emerging UI paradigms. Currently exploring Ripple, Solid, and Remix 3, and building my own agentic coding loops.
Experience
Lead Software Engineer | Founding Engineer (Wallet & Web)
- Created Zerion Wallet Extension: Owned the end-to-end architecture, security layer (private key encryption via SubtleCrypto, ensuring non-custodial private key safety for 200k+ users), and dapp communication protocol. Scaled the product from zero to one, competing directly with MetaMask and Rabby.
- Industry Authority (EIP-6963): Co-authored EIP-6963 (Multi-Injected Provider Discovery) alongside engineers from MetaMask and WalletConnect to standardize wallet-to-web interactions.
- Full-Stack & Infrastructure Leadership: Designed and owned data contracts for high-traffic portfolio and swap endpoints. Scaled CI/CD infrastructure on Google Cloud, automating isolated preview domains for rapid cross-team testing. Responsible for hiring Frontend Engineers.
- Business Impact: Helped the company raise Series A and B rounds.
Tech Stack: TypeScript, React, React Query, ethers.js, WebSockets, SubtleCrypto, Playwright.
Source Code: github.com/zeriontech/zerion-wallet-extension/
Open Source: defi-sdk-js — WebSocket data-fetching library
Senior Frontend Engineer
A UI for creating chatbots for Facebook Messenger.
- Performance: Rewrote the live chat feature to handle very large dialogs. Implemented bidirectional virtualization with binary search, turning a crashing UI into a snappy experience.
- Architecture: Created a UI kit / pattern library used across the project. Drove REST to GraphQL migration.
- Accessibility: Championed and implemented a11y best practices across the team.
Tech Stack: React, TypeScript, GraphQL (Apollo, Backend-for-Frontend), React Router, Jest, Mocha, Puppeteer.
Senior Developer | Performance Architect
- High-Throughput Trading UI: Refactored real-time trading UI to maintain 60fps under 200+ WebSocket messages/sec (peak) via Web Workers.
- Performance Optimization: Reduced initial load times by offloading heavy calculations to Web Workers and implementing sophisticated client-side caching with IndexedDB.
Tech Stack: React, Redux, TypeScript, WebSockets, IndexedDB, TradingView integration.
Software Engineer, Frontend
A social network with microtransactions. Main challenge: implementing 3D-Secure microtransactions into an infinite-scrolling social feed.
Tech Stack: Angular.js, React, Flux, jQuery.
Software Engineer
Airline ticket search system. Built a Single Page App handling large ticket and airline datasets. Implemented 3D-Secure payments, complex page transition animations, and website internationalization.
Tech Stack: Angular.js, jQuery, Gulp, Less.
Core Competencies
Architecture
- Scalable Frontend Systems
- Protocol Design
- Browser Extension Security
Performance
- Real-time Data Visualization
- Sub-100ms UI Latency
- Low-level Web Platform APIs
Leadership
- Technical Vision
- Hiring High-Output Teams
- Open Source Contributions
Skills and Technologies
- JavaScript / TypeScript
- AI Tooling & Agentic Systems
- Software Architecture & Design Patterns
- React
- Fullstack Development
- Bundlers: Vite, Rollup, Webpack, Parcel
- CI/CD, Cloud Infrastructure (Google Cloud)
- React Query, React Router, Immer.js
- SubtleCrypto / Web Crypto API
- ethers.js, web3.js, Ethereum, Solana
- Interaction Design
- Single Page Applications / PWAs
- Extensible Software
- SSR, Next.js, Remix, TanStack Start
- Accessibility (a11y)
- HTML / CSS / SVG
- Browser Extension Development
Education
Master of Science, Thermodynamics