Serhii.Get in touch
[ Germany ]Open to work

Serhii Valko

Frontend Engineer based in Germany. 5+ years shipping React, TypeScript, and React Native across FinTech, HealthTech & SaaS.

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The pipeline

Code with AI in the loop — not as a crutch, as a colleague.

01 · Claude Code

Claude Code

I plan, draft, and refactor inside an AI-paired editor. Specs become PRs without context-switching.

02 · MCP Servers

MCP Servers

Custom Model Context Protocol servers wire my tools — React devtools, GitHub, and design systems — into the agent loop.

03 · n8n Automation

n8n Automation

Webhook-triggered flows handle PR review, deploys, and content syndication. The boring parts run themselves.

04 · React / RN

React / RN

Production interfaces for FinTech, HealthTech, and SaaS. TypeScript-strict, performance-tuned, accessibility-first.

05 · Production

Production

Apps used by 10K+ daily users. Cold-start −25%, deploy time 15min → <5min, review cycle −50%.

Selected work

Three numbers I'm proud of.

Each case study below is a real production engagement with measured impact — performance, architecture, or shipping velocity. No fluff numbers.

01 · HealthTech · TenThousand · 2022 — 2023

React Native cold-start −25%

−25%
cold-start TTI
−40%
state boilerplate (Redux → MobX)
10+
screens on extracted hook lib
The problem

Heart-rate tracking app shipped with a 1.8s cold-start that violated the team's medical-grade UX SLA. Users dropped off before the first measurement screen rendered.

My approach

Audited the JS bundle and native init phase. Migrated React Native two minor versions, removed 100+ deprecation warnings, deferred non-critical native modules, and preloaded the heart-rate service before the JS bundle parsed.

Stack
React NativeTypeScriptMobXHermesMetro
Read the full story
02 · SaaS · SolidWay · 2023 — Present

CI/CD: 15 min → <5 min

<5 min
deploy time
−50%
review cycle time
4 → 8
PRs/day shipped
The problem

Deploy pipeline took 15+ minutes per merge, blocking 4 engineers from shipping in parallel. Caching was misconfigured; tests ran serially.

My approach

Reworked the pipeline: per-package install caching, parallel test shards, conditional builds for changed packages only, and deploy-on-tag workflow. Established PR-template + CODEOWNERS for review velocity.

Stack
GitHub ActionsVercelDockerpnpmTurborepo
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03 · SaaS · SolidWay · 2024 — Present

Component library across 3 squads

−30%
UI duplication
+40%
Time-to-Interactive
3 squads
shared adoption
The problem

Three product squads were each rebuilding the same primitives (Button, Modal, Input, Table). UI duplication ate review time and design QA budget.

My approach

Architected a token-driven internal library with per-component tree-shaking, dark-mode without FOUC, and Storybook + Chromatic visual regression. Adopted as the default by all 3 squads in 2 quarters.

Stack
React 18TypeScriptViteStorybookChromatic
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See all work — production + open-source
Experience

The path so far.

  1. 2023 — Present · Remote
    React Developer
    @ SolidWay
    • Architected component library adopted across 3 squads — −30% UI duplication
    • Memoization + lazy loading + code splitting → Time-to-Interactive +40%
    • Led PR standards for 4 engineers → review cycle −50%
    • CI/CD rework → deploy time 15min → <5min
  2. 2022 — 2023 · Kyiv, Ukraine
    React Native Developer
    @ TenThousand
    • Built medically compliant heart-rate tracking app
    • RN version migration → cold-start −25%
    • Redux → MobX refactor → state boilerplate −40%
    • Extracted hook library reused across 10+ screens
  3. 2021 — 2022 · Kyiv, Ukraine
    React Native Developer
    @ Jauntsoft
    • Real-time chat app with messaging SDK + push notifications · 10K+ DAU
    • Interactive data visualization dashboard for enterprise clients
    • Software cost estimation platform adopted by 50+ companies
Stack

What I reach for.

The tools that make it onto every project. Hover to see the details.

6 tools
Languages
Hover to view
Languages
  • TypeScript ·
  • JavaScript (ES6+) ·
  • HTML5 ·
  • CSS3 ·
  • Sass ·
  • LESS ·
9 tools
Frontend
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Frontend
  • React ·
  • React Native ·
  • Next.js ·
  • Redux ·
  • Redux Saga ·
  • MobX ·
  • Zustand ·
  • React Hook Form ·
  • Formik ·
6 tools
UI / Styling
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UI / Styling
  • Tailwind CSS ·
  • MUI ·
  • Styled Components ·
  • Framer Motion ·
  • GSAP ·
  • Three.js / R3F ·
7 tools
Data / API
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Data / API
  • REST ·
  • GraphQL ·
  • Apollo Client ·
  • Axios ·
  • TanStack Query ·
  • WebSockets ·
  • Socket.io ·
6 tools
Backend / DB
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Backend / DB
  • Node.js ·
  • Express ·
  • MongoDB ·
  • MySQL ·
  • PostgreSQL ·
  • Firebase ·
6 tools
Testing / QA
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Testing / QA
  • Jest ·
  • RTL ·
  • Cypress ·
  • Playwright ·
  • Storybook ·
  • ESLint ·
7 tools
DevOps / Tools
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DevOps / Tools
  • Git ·
  • Docker ·
  • GitHub Actions ·
  • Vercel ·
  • Webpack ·
  • Vite ·
  • Turborepo ·
7 tools
AI / Automation
Hover to view
AI / Automation
  • Claude Code ·
  • OpenAI Codex ·
  • Cursor ·
  • GitHub Copilot ·
  • MCP ·
  • n8n ·
  • AI Agents ·
Get in touch

Let's build something remarkable.

Open to Senior Frontend roles, contract work, and AI-augmented engineering collaborations. Based in Germany, available for remote and relocation.

Email meLinkedIn
Or directly
valkoserhii@gmail.com