Sergii Kryvenko
Sergii Kryvenko

Senior Frontend Engineer

Actively looking · Member since 8 Jun 2026
Message
Location
Ukraine
Desired salary
Unspecified
Work preference
Contract, Full Time
Experience level
Not set

About

Professional summary

I am a Senior Frontend Engineer and Tech Lead with over 10 years of experience architecting scalable SaaS web applications using React, TypeScript, and Next.js. I specialize in building production-grade UI systems, component libraries, design systems, and delivering end-to-end products for SaaS, B2B, and B2C platforms at scale.

My expertise lies in frontend architecture, state management, and data-layer design using Redux Toolkit, TanStack Query, GraphQL, and REST APIs. I focus on building high-performance applications optimized for Core Web Vitals, WCAG accessibility standards, and SEO.

I have led and mentored teams ranging from 4 to 14 engineers, driving technical direction and shipping business-critical features in Agile environments. I am experienced in integrating AI/LLM capabilities such as OpenAI GPT and Google Gemini APIs to automate workflows and enhance user experience.

Throughout my career, I have architected scalable React applications from scratch, improved legacy systems, and optimized performance and accessibility across multiple product surfaces. I have worked on diverse projects including SaaS widget builders, edtech platforms, cross-chain decentralized exchanges, and cloud gaming platforms.

I am passionate about delivering clean, maintainable code and scalable frontend architectures while fostering collaboration and technical growth within teams. I continuously seek to leverage modern technologies and best practices to build impactful and user-friendly web applications.

Skills

9 capabilities

Experience

Career history

Senior Frontend Engineer / Lead Opinion Stage

Architected a scalable React application from scratch using feature-based architecture, reusable components, and modular state management for a SaaS widget builder platform. Replaced a legacy content editor with a modern React-based solution, improving performance, maintainability, and workflow usability across the platform. Improved Core Web Vitals (LCP, CLS, INP) and adopted WCAG 2.1 AA accessibility standards across multiple product surfaces. Integrated AI/LLM capabilities using OpenAI GPT and Google Gemini APIs, automating content workflows and reducing manual processing time by 60%.

Senior Frontend Engineer / Tech Lead Upwork

Spearheaded React and TypeScript frontend solutions as a freelance Tech Lead across 5+ client engagements over 2 years. Released AI-powered SaaS platforms, warehouse management systems, and data visualization tools — owning architecture decisions, stakeholder communication, and delivery timelines independently. Incorporated AI features using OpenAI GPT and Google Gemini, automating workflows and enhancing user experience across multiple client products.

Senior Frontend Engineer / Lead Syndicode | Evrlearn

Led React and TypeScript frontend development for a personalized edtech learning discovery platform. Designed advanced search, filtering, and recommendation systems processing 10k+ course catalog entries with fast, responsive UX at scale. Optimized query performance with React Query, reducing perceived load times by up to 40% across data-heavy views.

Senior Frontend Engineer / Lead ClearCryptos

Engineered the React frontend for a cross-chain DEX with real-time swap aggregation across 5+ blockchain protocols. Shipped multi-chain portfolio analytics and the platform's first fiat on-ramp integration, expanding payment coverage by 100%. Unified the UI experience across 3 independently deployed platform surfaces (React, Blazor).

Frontend Engineer Syndicode | MedYouCate

Introduced SSR with Next.js on a medical education platform, improving SEO and content delivery speed by 35%. Created interactive medical case studies using React and refactored the platform to meet WCAG 2.1 AA accessibility standards.

Frontend Engineer Syndicode | Fuzu — Africa's #1 Career Platform

Scaled the React and MobX UI for Africa's leading career platform serving 100k+ monthly active users. Reduced initial load times by 30%+ in low-bandwidth (2G/3G) environments for mobile users across B2B and B2C surfaces. Built real-time data visualization using React Spring and Canvas API for interactive career insights and job market trends.

Frontend Engineer (Contract) Google | Google Stadia

Built performance-critical React UI for Google Stadia's cloud gaming platform. Delivered real-time game streaming interfaces at 4K/60fps with sub-100ms input latency under strict SLAs. Tuned React rendering pipelines and applied code-splitting to meet demanding performance requirements for a global gaming audience.

Frontend Engineer AppClose / Casetack

Shipped 10+ core features for a React-based co-parenting app, building shared calendars, real-time messaging, and collaborative task flows across 3+ user roles.

Frontend Engineer Syndicode | Senden 24 GmbH

Owned frontend delivery for an on-demand B2B logistics platform, building real-time dispatch and tracking interfaces used by 50+ operators daily. Added route optimization features using Canvas API and GSAP, improving operational efficiency for logistics operators.

Frontend Engineer Syndicode | Movinga

Developed reusable JavaScript/jQuery UI components and interactive booking calculators for a microservices moving platform, maintaining consistency across 5+ independently deployed services.

Frontend Developer Wargaming

Coded Canvas API and AngularJS interactive map features for World of Tanks, serving 4.5M+ players with real-time territory control and statistics.

Frontend Developer BIG DIG | Settle

Launched mobile-first payment and loyalty reward interfaces for a fintech startup, delivering contactless payment flows, real-time transaction status, and rewards UX.

Frontend Developer Coderoom | Visa GlobalBonus

Crafted modular JavaScript/jQuery components for Visa's global cardholder loyalty platform serving millions across 30+ countries, covering reward browsing, redemption, and partner offer flows.

Frontend Developer Coderoom | Data Group

Produced JavaScript/jQuery admin dashboards and real-time data visualization tools for internal analytics platforms, serving 20+ analysts.

Education

Learning history

Ivan Ogienka Kamianets-Podilsky National University

Master of Computer Engineering in Information Technology and Programming

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