Andrii Sirko Get in touch

Freelance since 2019 · open for the next contract

Andrii Sirko

Senior Frontend Engineer Full-Stack Contractor

Ten years of React in production, freelance since 2019 on multi-year and repeat engagements. I take on frontends that have to hold up — large monorepos, real traffic, and teams that need a system rather than a patch.

Get in touch See the outcomes
Years shipping
12
Years freelance
7
Peak MAU
40M+
Markets served
90+

Outcomes

What changed
because I was there.

Six results where the before and after are easy to state. The full record, client by client, follows below.

  1. MehrwerkFrontend Lead · team of 5

    4 mo → 30 min

    Client onboarding became a configuration task

    Designed a multi-tenant React application framework that turned each new client from a four-month project into a half-hour of configuration.

    • React
    • Next.js
    • Ionic
    • GraphQL

  2. ABOUT YOU40M+ MAU e-commerce

    +5%

    Mobile add-to-basket rate, shipped to 100% of traffic

    Owned the add-to-basket CTA experiment end to end — SSR variant for multi-size products, size selection, captcha retry, a11y, Cypress E2E. The winning variant lifted the rate by 5% (relative).

    • React
    • TypeScript
    • SSR
    • Cypress

  3. ABOUT YOU40M+ MAU e-commerce

    Weeks → same day

    Frontend removed from the A/B experiment critical path

    Replaced per-experiment feature flags with prefix-based activation, so new experiments launch with no frontend release. Enables ~6 experiments a month across the growth and recommendation teams.

    • React
    • TypeScript
    • A/B testing

  4. Accenture · VW / AudiSenior React Developer

    90+ markets

    One dealer search, two automotive brands

    A white-label Dealer Search built for Volkswagen, then integrated into Audi as a micro-frontend rather than a fork. Live on Audi.de across more than ninety markets.

    • React
    • TypeScript
    • Micro-frontends
    • Webpack

  5. MehrwerkFrontend Lead · team of 5

    1M+ MAU

    Content updates without a developer in the loop

    Built a UI Editor that lets non-technical editors publish content changes to web and native apps in real time, for a platform with 1M+ monthly active users.

    • React
    • React Native
    • GraphQL
    • MongoDB

  6. ABOUT YOU40M+ MAU e-commerce

    ~120 icons

    Web/native icon gap closed in a single release

    Automated the migration of the shared icon set to the new icon system (Node.js, Figma REST API, PNG → SVG) — one regression-verified release, no changes for product teams.

    • Node.js
    • Figma REST API
    • Monorepo

Experience

One practice
since 2019.

Multi-year and repeat engagements for German and international product companies, and the full-time roles that came before.

Freelance Senior Frontend / Full-Stack Engineer

Freelancer / IT contractor · Remote, Germany

— Present

Multi-year and repeat engagements for German and international product companies. Clients and outcomes:

  • ABOUT YOU SE & Co. KG

    E-commerce, 40M+ MAU

    Senior Frontend Engineer · aboutyou.de

    • Removed frontend from the A/B experiment critical path: replaced per-experiment feature flags with prefix-based activation, so new experiments launch with no frontend release — lead time down from days–weeks (ticket, sprint, deploy) to same-day self-serve. Enables ~6 experiments/month across the growth and recommendation teams.
    • Owned the mobile add-to-basket CTA experiment end to end: SSR variant for multi-size products, size selection, captcha retry, a11y, Cypress E2E. Winning variant lifted mobile add-to-basket rate by 5% (relative), shipped to 100% of traffic.
    • Delivered the loyalty Status Program end to end into the Coins wallet — gRPC integration, deep-linked entry points for campaigns, mobile and desktop — from API contract to 100% production rollout. Storybook and integration coverage across every tier and error state.
    • Closed the web/native icon gap: automated migration of ~120 shared icons to the new icon system (Node.js, Figma REST API, PNG → SVG) in a single regression-verified release, no changes for product teams.

    Stack React · TypeScript · Linaria · gRPC · Monorepo (Yarn workspaces) · Node.js · Storybook · Jest · RTL · Cypress · GitLab CI · Datadog

  • Mehrwerk GmbH

    B2B2C loyalty & content platform, 1M+ MAU

    Frontend Lead · team of 5 · mehrwerk.de

    • Owned the platform architecture: designed a multi-tenant React application framework that cut client onboarding from ~4 months to 30 minutes, turning each new client into a configuration task instead of a project.
    • Built a UI Editor that let non-technical editors publish content changes to web and native apps in real time, removing developer involvement from content updates for 1M+ monthly active users.
    • Designed and owned the k6/Grafana Cloud load-testing suite (smoke, stress, soak, spike) for SSR and GraphQL services, giving every release a measured capacity limit before it hit production.
    • Led the WCAG accessibility migration across web and native apps — audit, remediation standards, implementation — bringing the platform to compliance required by enterprise clients.

    Stack TypeScript · React · Vue 2/3 · Ionic · React Native · Next.js · Node.js · Kotlin · GraphQL · MongoDB · Jest · Cypress · AWS · k6

  • SelectCode GmbH

    meinGPT, enterprise AI platform

    Fullstack Developer · meingpt.com

    • Built collaborative features — shared AI assistants and chat workflows — for a privacy-focused RAG platform with multi-LLM support (React, Zustand).
    • Implemented secure tRPC/Prisma endpoints for organisation hierarchies, RBAC (Lucia Auth) and Stripe subscriptions — the billing and permission layer enterprise customers are sold on.

    Stack TypeScript · React · NestJS · tRPC · Prisma · PostgreSQL · Playwright · RAG · OpenAI API · Kubernetes

  • eBay GmbH (Adevinta)

    Kijiji Autos, Canada’s largest auto marketplace

    Senior React Developer · dealer retail team · kijijiautos.ca

    • Delivered React features across the dealer-facing product surface used by Canadian car dealers to manage and sell inventory.

    Stack React · TypeScript · Jest · TestCafe · AWS

  • Accenture

    Automotive clients — VW, Audi, smart / Daimler

    Senior React Developer

    • Implemented a white-label Dealer Search app for VW and integrated it into Audi via micro-frontends — live on Audi.de across 90+ markets.
    • Built the smart IAA landing page with immersive animated React components for the brand’s future product reveal.

    Stack React · TypeScript · Styled Components · Webpack · AEM · Jest

  • Factor Eleven

    Ad-tech

    Senior React Developer · factor-eleven.de

    • Architected the React-based AdManager application and a shared UI library reused across the company’s products, so new features were built once and shipped everywhere.

    Stack React · GraphQL · Apollo · Jest · Enzyme · Cypress · SASS · CSS Modules · Webpack · GitLab

  • lemon.markets

    Fintech

    Senior React Developer · lemon.markets

    • Built Prismic-powered Blog and CMS pages in Next.js, letting the marketing team publish without engineering support.

    Stack React · Next.js · TypeScript · Prismic

  • ToolTime

    Field-service SaaS

    Senior React Developer · tooltime.de

    • Designed and implemented a React/GraphQL field-service management application for tradespeople.

    Stack TypeScript · React · GraphQL · Apollo · Jest · Cypress · CircleCI · AWS

Before the practice — full-time roles

  • Careem (acquired by Uber)

    Ride-hailing & delivery super-app

    —

    Senior Software Developer · Full-time · Berlin · careem.com

    • Led frontend architecture for the corporate-customers product and maintained the shared Web UI library used across the Careem ecosystem.
    • Contributed to last-mile delivery and CareemNow (food delivery) on a platform handling 380M+ requests a day for 10M+ monthly active users; Scrum master for a team of 6.

    Stack React · React Native · Redux · Saga · TypeScript · Jest · Cypress · Kotlin · Scala · MySQL · AWS · Docker · Jenkins

  • Circula GmbH

    Expense management

    —

    Frontend Developer · Full-time · Berlin · circula.com

    • Built expense-management tools for accountants and supervisors (React, Redux, Ruby on Rails).

    Stack React · Redux · Ruby on Rails · RSpec · Docker

  • Mes.mo GmbH / Gastroguide

    Restaurant SaaS

    —

    Full Stack Developer · Full-time · Stuttgart · gastroguide.de

    • Architected the restaurant platform: reservation system, website constructor, advertising system, form/menu builders and REST API for mobile apps. 15 restaurants on the platform.

    Stack React · Redux · Flux · PHP · MySQL · AWS

  • UKEESS

    E-commerce agency

    —

    Full Stack Developer · Full-time · Lviv, Ukraine

    • Developed and maintained Magento plugins for e-commerce clients (PHP).

    Stack Magento · PHP

Live demo

Ask the CV a question.
Watch the page answer.

A voice agent that knows this CV and drives the UI while it talks — a small, production-shaped ElevenLabs Agents integration in a real React app.

Ask “What did Andrii build at Mehrwerk?” and the matching project card lights up on screen. The agent answers from a RAG knowledge base over the CV. The browser never sees an API key: a Next.js route mints a short-lived signed URL, throttled per IP, and the session opens over WebSocket from there.

There is a text mode, so no microphone is needed. The agent, its tools and the knowledge base are code in the repo, pushed with the ElevenLabs CLI, with unit tests on the tool handlers, transcript and throttle.

Open the demo Read the source
  • Next.js
  • TypeScript
  • ElevenLabs Agents
  • RAG
  • Tailwind
  • Vitest
  • Vercel

Client tools the agent can call

highlightProject{ projectId }
Scrolls to the project card and highlights it. Blocks until the UI confirms, so the agent says what actually happened.
filterByTech{ tech }
Filters the grid by stack and returns the match count — “three projects used GraphQL” comes from the DOM, not the model.
showContactno params
Reveals the contact panel.

Stack

Tools, and where they were used

Pick anything below to see which clients and roles it was used for — the answer appears in the experience section above.

About

Ten years, one discipline

I’ve run one freelance practice since 2019 — long engagements, and clients who come back — which means I join codebases that already have history and constraints. The job is rarely a rewrite. It’s reading what’s there, finding the seam, and leaving the team with something they can extend after I’m gone.

I’m based in Berlin, Germany, and work remotely across European time zones. Ukrainian is my first language; I work in English and German.

Education

Lviv Polytechnic National University

MSc Computer Science · 2010 — 2015

Thesis: a context-aware web service for booking personal services. Coursework included writing a compiler in C/Assembler and implementing virtual desktops for Windows 7 against the WinAPI.

Languages

  • Ukrainian Native
  • English Fluent · C1
  • German Fluent · C1

Away from the keyboard

  • PowerliftingCandidate Master of Sport
  • Reading25+ books a year
  • Travel30 countries
  • AlsoMotorcycling & 3D printing

Contact

Have something that
needs to hold up?

Contract, fractional lead, or a second opinion on an architecture decision — all fine. Or skip the email and ask the voice agent.

Phone +49 176 4340 4914 Call LinkedIn in/andrii-sirko Open GitHub andrii-sirko Open

Berlin, Germany · remote across Europe · CV in plain text