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I’m a staff-level full-stack engineer and tech lead with 16+ years of experience designing scalable SaaS platforms and high-performance web systems for enterprises and AI-driven products. I’ve delivered major performance and efficiency gains—often in the range of 10x to 52x—by refactoring front-end architectures, moving data fetching to Next.js Server Components, and applying deep re-render and component hierarchy optimizations across React/Next.js and Node.js ecosystems. I lead engineering teams (up to 10 engineers), build from MVP through acquisition, and bring strong expertise in AI/LLM integration, system design, and large-scale, high-volume data platforms. My work also spans secure enterprise identity and multi-tenant authentication (Auth0, WorkOS, SSO, RBAC), test automation (Playwright, Vitest/Jest), and production-grade delivery with strong engineering discipline—from type safety and linting to observability and CI-friendly practices.…I’m a staff-level full-stack engineer and tech lead with 16+ years of experience designing scalable SaaS platforms and high-performance web systems for enterprises and AI-driven products. I’ve delivered major performance and efficiency gains—often in the range of 10x to 52x—by refactoring front-end architectures, moving data fetching to Next.js Server Components, and applying deep re-render and component hierarchy optimizations across React/Next.js and Node.js ecosystems. I lead engineering teams (up to 10 engineers), build from MVP through acquisition, and bring strong expertise in AI/LLM integration, system design, and large-scale, high-volume data platforms. My work also spans secure enterprise identity and multi-tenant authentication (Auth0, WorkOS, SSO, RBAC), test automation (Playwright, Vitest/Jest), and production-grade delivery with strong engineering discipline—from type safety and linting to observability and CI-friendly practices.

Valyefim Yefimov

Full Stack Developer, Front-End Developer, Back-End Developer, +6

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I’m a staff-level full-stack engineer and tech lead with 16+ years of experience designing scalable SaaS platforms and high-performance web systems for enterprises and AI-driven products. I’ve delivered major performance and efficiency gains—often in the range of 10x to 52x—by refactoring front-end architectures, moving data fetching to Next.js Server Components, and applying deep re-render and component hierarchy optimizations across React/Next.js and Node.js ecosystems. I lead engineering teams (up to 10 engineers), build from MVP through acquisition, and bring strong expertise in AI/LLM integration, system design, and large-scale, high-volume data platforms. My work also spans secure enterprise identity and multi-tenant authentication (Auth0, WorkOS, SSO, RBAC), test automation (Playwright, Vitest/Jest), and production-grade delivery with strong engineering discipline—from type safety and linting to observability and CI-friendly practices.…I’m a staff-level full-stack engineer and tech lead with 16+ years of experience designing scalable SaaS platforms and high-performance web systems for enterprises and AI-driven products. I’ve delivered major performance and efficiency gains—often in the range of 10x to 52x—by refactoring front-end architectures, moving data fetching to Next.js Server Components, and applying deep re-render and component hierarchy optimizations across React/Next.js and Node.js ecosystems. I lead engineering teams (up to 10 engineers), build from MVP through acquisition, and bring strong expertise in AI/LLM integration, system design, and large-scale, high-volume data platforms. My work also spans secure enterprise identity and multi-tenant authentication (Auth0, WorkOS, SSO, RBAC), test automation (Playwright, Vitest/Jest), and production-grade delivery with strong engineering discipline—from type safety and linting to observability and CI-friendly practices.

Available to hire

I’m a staff-level full-stack engineer and tech lead with 16+ years of experience designing scalable SaaS platforms and high-performance web systems for enterprises and AI-driven products. I’ve delivered major performance and efficiency gains—often in the range of 10x to 52x—by refactoring front-end architectures, moving data fetching to Next.js Server Components, and applying deep re-render and component hierarchy optimizations across React/Next.js and Node.js ecosystems.

I lead engineering teams (up to 10 engineers), build from MVP through acquisition, and bring strong expertise in AI/LLM integration, system design, and large-scale, high-volume data platforms. My work also spans secure enterprise identity and multi-tenant authentication (Auth0, WorkOS, SSO, RBAC), test automation (Playwright, Vitest/Jest), and production-grade delivery with strong engineering discipline—from type safety and linting to observability and CI-friendly practices.

Skills

Experience Level

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Expert

Intermediate

Intermediate

Intermediate

Language

Ukrainian

Fluent

English

Fluent

Russian

Fluent

Work Experience

Staff Full-Stack Engineer & Tech Lead at Merly

September 1, 2024 - May 1, 2026

Cut page load time from ~3s to ~200ms by migrating data fetching to Next.js Server Components, removing client-side request waterfalls. Improved UI rendering performance by 10x through re-render optimizations, memoization, and component hierarchy refactoring. Increased automated test coverage from 0% to 50% using unit, integration, and Playwright E2E tests to reduce regression risk. Implemented SSO with Auth0 (with backend components) and introduced Chakra UI, enabling ~5x faster feature development. Enforced strict TypeScript typing and ESLint standards, eliminating unsafe `any` usage across the codebase.

Lead/Senior Full Stack Engineer at Merly

September 1, 2024 - Present

Drove platform-wide performance and quality improvements across the Merly product; reduced page load time from 3 seconds to 200ms by migrating data fetch to Next.js Server Components; achieved a 10x improvement in UI rendering via targeted optimization and component refactoring; introduced skeleton loaders and strict TypeScript typing; strengthened code quality with ESLint rules; expanded unit and integration test coverage to ~50%; implemented end-to-end testing with Playwright; introduced Redux for global state and Chakra UI for faster UI development; documented architecture in Jira/Confluence; implemented RBAC and multi-tenant architecture; improved deployment and observability.

Senior Full-Stack JS Staff Engineer at Merly

September 1, 2024 - Present

Responsible for platform-wide performance and quality improvements across the Merly Mentor product, contributing to technical excellence and developer experience. Led initiatives to optimize data fetching and server rendering, introduced scalable front-end loaders, and elevated code quality through disciplined TypeScript usage and linting. Implemented end-to-end testing with Playwright and introduced a Chakra UI-based component library to accelerate feature development. Drove architectural decisions for multi-tenant AI-enabled SaaS platform design and defined long-term reliability strategies.

Senior Full-Stack Engineer at Merly, USA

September 1, 2024 - Present

Drove platform-wide performance and quality improvements across the Merly Mentor product, contributing to both technical excellence and developer experience. Rebuilt the browser extension from vanilla JS to a React-based solution, achieving faster development cycles and a more robust UI. Implemented Redux for global state management, introduced Chakra UI for consistent UI primitives, and expanded unit and integration coverage to reduce regressions.

Senior Full-Stack Engineer at Merly

September 1, 2024 - Present

Senior Full-Stack JS Staff Engineer responsible for platform-wide performance and quality improvements across Merly Mentor product. Led optimizations such as reducing page load times, introducing skeleton loaders, and implementing end-to-end tests to improve release confidence and user experience. Built Chakra UI-driven UI blocks and React/Next.js acceleration strategies, and led a team of engineers through full product lifecycle.

Lead/Senior Full Stack Engineer at Platform.ai

September 1, 2023 - August 31, 2024

Led design and delivery of the Platform.ai MVP from scratch; built a Chrome/Edge browser extension enabling clinicians to retrieve patient information within their browser workflow to support early-stage fundraising. Architected full system: user lifecycle management, RBAC, activity tracking, and multi-tenant data isolation for an AI-driven SaaS platform. Rebuilt the browser extension from vanilla JS to React/Plasm o, achieving 10x development velocity; integrated Chakra UI v2; grew unit/integration test coverage to 80%; implemented Redux for global state; introduced AI assistant leveraging OpenAI; implemented SSO with corporate ID; implemented robust data access controls.

Senior Full-Stack JS Engineer at Merly, USA

September 1, 2023 - September 1, 2024

Led design and delivery of the Platform Flow.ai MVP from scratch, a health-care Chrome/Edge extension enabling clinicians to retrieve patient information directly within their browser workflows, supporting early-stage fundraising.

Lead/Senior Full-Stack Engineer at Platformflow.ai

May 1, 2023 - September 1, 2024

Led the Platformflow.ai MVP from scratch: a healthcare clinician Chrome/Edge extension supporting early-stage fundraising. Architected a multi-tenant user lifecycle, RBAC, and Auth0-based authentication across Next.js, NestJS, and the browser extension environment. Rebuilt the extension from vanilla JS to Plasmo + React, achieving ~10x development velocity on a complex, math-heavy product. Grew test coverage from 0% to 80% (unit, integration, and Playwright E2E) across critical patient-data workflows. Built an in-extension AI assistant (OpenAI) enabling conversational patient data queries for clinicians and reducing context switching.

Lead Design and Delivery at Platflow.ai

May 1, 2023 - September 1, 2024

Led the design and delivery of the Platflow.ai MVP, an AI-powered SaaS for clinicians, including architecture, RBAC, activity tracking, and multi-tenant user management. Built full-stack features, re-architected components for rapid iteration, and established long-term platform strategy.

Lead/Senior Full-Stack Engineer (Consulting) at Independent Consulting (Confidential Clients)

October 1, 2020 - October 1, 2025

Scaled a high-load Firebase chat platform processing millions of records daily with ~5M new active users annually, on infrastructure exceeding 60TB of production data. Designed Firebase data structures, indexing strategies, security rules, and automated access-control tests to sustain real-time performance at scale. Shipped multiple production Manifest V3 browser extensions (service workers, content scripts, runtime messaging) while minimizing re-renders and DOM-observer overhead. Built cloud functions and Node.js/TypeScript backend services including event-driven Firebase triggers and automation workflows. Delivered frontend applications and internal platforms in Angular, React, TypeScript, RxJS, and GraphQL; implemented Cypress E2E testing covering UI, auth, and regression flows across client projects.

Lead/Senior Full-Stack Engineer at Dinghy

February 1, 2018 - May 1, 2023

Owned architecture of a layer-2 middleware coordinating UI and backend services, including auth flows, request orchestration, and data normalization. Introduced static typing (Flow) across a React codebase to cut runtime type errors by 10x. Built a dynamic, rule-based frontend form engine, reducing product configuration delivery cycles from months to weeks. Contributed to a platform that achieved two acquisitions, with final acquisition by Kingsbridge Insurance.

Lead/Senior Full Stack Engineer at Dinghy (UK)

February 1, 2018 - May 1, 2023

Designed and delivered front-end and back-end systems, including a modern SPA architecture, robust API layer, and multi-tenant data model. Introduced Jest and Playwright-based testing, implemented server-side rendering improvements, and drove overall code quality with strict TypeScript typing. Led cross-functional teams to align on architectural decisions and ensure timely delivery of features.

Lead/Senior Frontend Developer at Dev-Pronet

February 1, 2012 - February 1, 2018

Promoted from Junior Engineer to Team Lead; led cross-functional frontend/backend teams of up to 10 engineers. Reduced SQL query counts from ~1,300 to ~25 per operation (52x efficiency improvement) through query profiling and indexing. Selected technology stacks that improved development velocity by up to ~15x on key products. Drove test coverage to 95%+ across multiple projects, achieving near-zero production bug rates. Contributed to a ~500-contributor enterprise digital operations system (DOS) built in TypeScript.

Lead / Senior Front-End Developer (PHP/JS) at Gameloft, Ukraine

February 1, 2012 - February 1, 2018

Led design and delivery of mid-tier and front-end systems; managed cross-functional front-end and back-end teams of up to 12 engineers; established clean API contracts and robust data flows. Orchestrated SPA architecture during a period when single-page apps were emerging, delivering highly interactive, desktop-class UX in the browser. Implemented robust error handling, improved data validation, and contributed to architectural decisions that scaled across multiple products. Pioneered multi-team collaboration and contributed to global hiring assessments and platform initiatives.

Principal Lecturer at International Solomonov University

September 1, 2011 - December 1, 2013

Taught undergraduate software development courses including HTML, CSS, JavaScript, PHP, MySQL, and Zend Framework, and covered SDLC best practices.

Principal Lecturer at International Solomonov University, Ukraine

September 1, 2011 - December 1, 2013

Taught core software development disciplines to undergraduate students, covering HTML, CSS, JavaScript, PHP, MySQL, and Zend Framework. Delivered practical training on SDLC, project management, and structured development methodologies, blending academic instruction with hands-on implementation.

Full-Stack Developer (PHP/JS) at Gameloft

June 1, 2010 - February 1, 2012

Built a company-wide Meeting Room Booking System with LDAP-integrated RBAC, used as the primary corporate calendar across global offices. Pioneered SPA architecture within the organization using ExtJS/YUI, delivering a desktop-class browser experience. Built a global candidate assessment platform across studios with anti-cheat safeguards and automated scoring.

Full Stack Developer at Gameloft (Ukraine)

June 1, 2010 - February 1, 2012

Built high-traffic internal tools and dashboards for Gameloft studios; designed a company-wide Meeting Room Booking System; implemented LDAP-based authentication and role-based access control; migrated from legacy ExtJS/YUI to modern React/JS/TypeScript stack; contributed to backend services with Node.js; improved data models and real-time capabilities for internal workflows.

Full Stack Developer (PHP/JS) at Gameloft, Ukraine

June 1, 2010 - February 1, 2012

Built high-traffic internal enterprise tools for thousands of daily users across Gameloft’s global offices, focusing on reliability, data integrity, and real-time responsiveness. Designed and implemented a company-wide Meeting Room Booking System; implemented authentication and role-based access control integrated with LDAP; pioneered SPA approaches using ExtJS/YUI to deliver desktop-class UX in the browser. Designed and optimized MySQL schemas for performance, implemented PHP business logic to support scheduling workflows, and collaborated with stakeholders to evolve product systems and a company-wide recruitment assessment platform.

Full Stack Developer (PHP/JS) at Gameloft

June 1, 2010 - February 1, 2012

Built high-traffic internal tools across Gameloft’s global offices focused on reliability, data integrity, and real-time responsiveness. Implemented full-stack solutions using PHP/JS, designed scalable backend services and robust frontend interfaces.