JSON-to-Something
A fully client-side developer toolbox for converting JSON to TypeScript, Zod, and JSON Schema, plus YAML to Nginx or Envoy configs with shareable state and local history.
Available for new projects
Valentyn Yefimov
Staff Software Engineer / Tech Lead | 16+ Years
Staff software engineer specializing in React, Next.js, Angular, and Node.js. I build high-performance, reliable systems from MVP to enterprise scale.
Budva, Montenegrovalentine.efimov@gmail.com
About Me
Core Strengths
Proven track record leading teams in large organizations with 400+ developers, building full ecosystems, and optimizing massive back-office platforms. Based in Budva, Montenegro - open to remote worldwide and ready to fly in for key meetings.
FE
Frontend
Pixel-perfect, responsive UIs with React/Next.js (App Router, SSR/SSG), TypeScript, Tailwind/MUI/Chakra, Framer Motion. Mobile via Capacitor/React Native.
BE
Backend
Node.js (Express/NestJS), REST/GraphQL APIs, high-load optimization processing 1M+ records/day.
DB
Databases
PostgreSQL, MongoDB, Redis at scale. Handled production clusters exceeding 60TB.
QA
Testing & Quality
Playwright/Cypress E2E, unit/integration testing, CI/CD with GitHub Actions, Docker containerization.
EX
Extras
Chrome/Edge extensions (MV3), Web3/smart contracts, SaaS/task platforms (Jira-like), Lighthouse 95+.
AI
AI Integration
AI-assisted prototyping only. Final architecture, security, performance tuning, and production code: 100% human.
Career
Work Experience
16+ years of delivering scalable full-stack solutions, from startups to enterprises with 500+ distributed engineers.
Full-Stack JS Staff Engineer
Merly, US
Sep 2024 - Present
United States (Remote)
- Drove platform-wide performance and quality improvements across the Merly Mentor product.
- Reduced page load time from ~3s to ~200ms by moving data fetching to Next.js Server Components and removing client waterfalls.
- Delivered a 10x UI rendering performance improvement through memoization, re-render control, and component hierarchy refactoring.
- Introduced skeleton loaders to improve perceived performance and user experience.
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- Configured and enforced ESLint rules to maintain high engineering standards and architectural consistency.
- Grew test coverage from 0% to 50% with unit and integration tests and added Playwright E2E for critical product flows.
- Contributed to interactive prototyping to validate ideas and accelerate iteration before full implementation.
- Enforced strict TypeScript standards and ESLint rules, removing unsafe any usage across the codebase.
- Implemented SSO (including backend components in Go) and improved authentication flows.
- Introduced Chakra UI primitives that accelerated feature delivery by ~5x with reusable, consistent components.
- Documented architecture, processes, and decisions in Jira and Confluence for long-term maintainability.
Lead/Senior Full Stack Engineer
Platflow.ai, US
May 2023 - Sep 2024
United States (Remote)
- Led design and delivery of the Platflow.ai MVP from scratch for a healthcare Chrome/Edge extension.
- Architected multi-tenant SaaS foundations: user lifecycle, RBAC, activity tracking, and scalable isolation from day one.
- Rebuilt extension architecture from vanilla JS to Plasmo + React, increasing development velocity by ~10x.
- Integrated Chakra UI 2 and reusable component patterns, reducing feature implementation time by ~5x.
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- Raised automated coverage from 0% to 80% with unit/integration tests plus Playwright E2E.
- Introduced Redux for global state management across the extension, improving architectural quality and reducing bug surface area.
- Built and maintained admin tooling via Retool for rapid prototyping of internal operational flows.
- Built an in-extension AI assistant (OpenAI integration) to query patient data conversationally.
- Designed modular architecture adaptable to shifting product requirements and UX goals.
Lead/Senior Full Stack Engineer
Dinghy, UK
Feb 2018 - May 2023
Kharkiv, Ukraine
- Owned architecture of middle-tier and frontend systems with clear separation of concerns and scalable structure.
- Implemented a Layer 2 Middle Tier for auth orchestration, request coordination, and data normalization.
- Introduced Flow static typing to React, reducing runtime type errors by ~10x.
- Built a dynamic rule-based form engine that cut configuration delivery cycles from months to weeks.
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- Introduced Jest coverage for core logic and UI, reducing production defects and increasing release confidence.
- Introduced Redux for application-wide state management across a complex multi-product form ecosystem.
- Collaborated closely with backend engineers to define clean API contracts, predictable data flows, and robust error handling.
- Actively contributed to Agile ceremonies and proactively surfaced risks, blockers, and architecture improvements.
- Helped deliver a platform acquired twice, with final acquisition by Kingsbridge Insurance.
Lead/Senior Front-End Engineer
Dev-Pro.net, Ukraine
Feb 2012 - Feb 2018
Kharkiv, Ukraine
- Promoted from Junior Engineer to Team Lead / Technical Lead with combined technical and people leadership.
- Led cross-functional teams of up to 12 engineers and drove hiring, onboarding, mentoring, and delivery quality.
- Authored technical specs and architecture proposals that accelerated implementation velocity by up to ~15x.
- Pushed test coverage to 95%+ on multiple projects, driving near-zero production bug thresholds.
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- Optimized SQL-heavy operations from ~1300 queries to ~25 per operation (about 52x improvement).
- Contributed to a large TypeScript enterprise initiative with ~500 distributed contributors.
- Designed and delivered enterprise workflow platforms similar to Asana/Jira with real-time collaboration capabilities.
- Provided technical leadership to clients on architecture decisions, technology selection, and long-term roadmap.
Principal Lecturer
International Solomonov University, Ukraine
Sep 2011 - Dec 2013
Kharkiv, Ukraine
- Taught SDLC, project management, and practical software engineering using HTML, CSS, JavaScript, PHP, MySQL, and Zend Framework.
- Combined academic instruction with hands-on implementation aligned to real production team workflows.
- Delivered structured training on collaboration workflows, quality standards, and production engineering practices.
- Prepared students for real-world software engineering roles through project-based practical education.
Full Stack Engineer (PHP/JS)
Gameloft, Ukraine
Jun 2010 - Feb 2012
Kharkiv, Ukraine
- Built high-traffic internal tools for thousands of daily users across global offices.
- Developed a company-wide Meeting Room Booking system used as the primary internal calendar.
- Implemented LDAP-based authentication and role access controls aligned with corporate security standards.
- Pioneered SPA architecture internally using ExtJS/YUI, delivering desktop-class interactivity in browser.
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- Designed and optimized MySQL schemas and query paths for high-frequency production usage.
- Implemented complex PHP business logic for scheduling workflows and scalable booking policies.
- Contributed to a global candidate-assessment platform used across Gameloft studios worldwide.
- Built and maintained back-office tools for question banks, weighted scoring logic, and reporting.
- Implemented secure, time-limited candidate testing flows with automated scoring.
- Supported multiple question formats including code, multiple-choice, and custom responses.
- Introduced anti-cheating mechanisms (including image-rendered code prompts) to reduce unauthorized execution.
- Ensured reliable progress and completion tracking metrics across global candidate sessions.
Tech Stack
Skills & Technologies
A comprehensive toolkit honed over 16+ years across dozens of projects and industries.
Frontend Development
AngularReactVueSvelteBackbone.jsKnockoutBootstrapMaterial DesignAnt DesignMUI
Mobile Development
CordovaIonicReact NativePhoneGapCapacitor
Backend Development
Node.jsPHPExpressNext.jsKoaNestJSPostgreSQLMySQLRedisMongoDB
CMS
WordPressButter CMSContentstackStrapi
Version Control
SVNGitGitHubGitLabBitbucket
Testing & Quality Assurance
PhantomJSCasperJSSlimerJSPuppeteerMochaProtractorKarmaJasmineJestCypress
Cloud & Hosting
AWSAzureGCPHerokuDigitalOceanVercelBluehostGoDaddyCloudflare
DevOps, PM & AI
DockerConvoxJiraTrelloClickUpAsanaPage Speed OptimizationGoogle PageSpeed InsightsVercel AIChatGPT
Background
Education & Awards
EDU
Education
Master's Degree, Software Engineering
International Solomonov University
2006 - 2011
Oracle 10g
International Solomonov University
2006 - 2008
Mathematical and Informational School
School No. 15
1995 - 2006
AWD
Awards & Certifications
PCI Awareness Certification
Payment Card Industry compliance
QuizIT Olympiad
Two-time honoree in IT knowledge competition
Languages
English (Full Professional)Ukrainian (Native)Russian (Native)
Open source
My open-source projects
I publish practical tools focused on measurable performance and maintainable frontend architecture. Here are a few projects you can use right now:
react-perf-hooks
A focused set of React performance hooks and examples for profiling render behavior and improving UI responsiveness with targeted optimizations.
chakra-ui3-tour
A guided product-tour implementation built around Chakra UI v3 patterns for onboarding and feature discovery flows.
string-best-match
A string matching utility focused on selecting the closest candidate with practical scoring for real-world search and mapping tasks.
Let's Connect
Ready for Complex Challenges
From idea to production, I bring 16+ years of experience building scalable systems. Open to travel worldwide for in-person meetings. Let's build something lasting.
Currently based in Budva, Montenegro