bartek@warsaw:~$ whoami

Bartłomiej Krok Development

▊

I design and build fast, reliable products for web and mobile. React, React Native and the tooling around them - from first commit to production.

get in touchwhat I doopen to new projects

01.about

I'm a software engineer and solution architect based in Warsaw, Poland. I work at Callstack - one of the leading React & React Native consultancies - where I build and ship apps used by millions of people.

I care deeply about performance, developer experience and code that stays readable a year later. From bundlers and build pipelines to release automation, I like to understand the whole path from commit to production.

Outside of work I spend time with my beloved family and support Liverpool FC. // YNWA

$ cat profile.json

{
  "name": "Bartłomiej Krok",
  "location": "Warsaw, PL",
  "roles": [
    "Software Engineer",
    "Solution Architect"
  ],
  "languages": ["pl", "en"],
  "supports": "Liverpool FC"
}

02.services

01

Web Development

Modern, fast web applications built with React, Next.js and TypeScript. From MVPs to production systems serving real traffic - with performance and maintainability baked in.

  • React
  • Next.js
  • TypeScript

02

Mobile Development

Cross-platform mobile apps with React Native. One codebase, native feel on iOS and Android. Smooth animations, offline support and app store delivery included.

  • React Native
  • iOS
  • Android

03

Solution Architecture

System design, technical audits and architecture reviews. I help teams choose the right tools, untangle legacy code and set up foundations that scale with the product.

  • System Design
  • Audits
  • Scalability

04

Performance & Tooling

Bundle size, startup time, build pipelines. I work on developer tooling and performance optimization - including bundlers and CI/CD - so your app and your team ship faster.

  • Bundlers
  • CI/CD
  • Optimization

03.stack

./languages

  • TypeScript / JavaScript
  • Swift / Objective-C
  • Kotlin / Java
  • C# (Unity)

./web

  • React
  • Next.js
  • Performance profiling
  • Web security
  • Payments (web & mobile)

./mobile

  • React Native
  • Navigation & deep linking
  • Reanimated · Lottie · Gesture Handler
  • Accessibility

./delivery & quality

  • CI/CD - Azure DevOps
  • Testing - e2e · unit · integration
  • Observability - RUM · error tracking
  • Performance audits

$ ls ./also-on-the-radar

  • Node.js
  • GraphQL
  • Re.Pack
  • Rock.js
  • webpack / Rspack / Turbopack
  • Expo
  • AWS
  • Docker
  • Unity
  • Rust
  • Go
  • WebAssembly
  • AI agents
  • Brownfield
  • TV & desktop

04.apps

Things I build after hours - small, useful and free to try.

$ open tree.bartekkrok.com

Family Tree↗

// your family history, one click at a time

A friendly family tree builder that runs entirely in your browser. Add people, link generations, pan and zoom through your ancestors - no account needed, your data stays with you. Simple enough for grandma, nerdy enough for you.

  • Vanilla JS
  • Privacy-first
  • Senior-friendly

05.contact

$ ./say-hello.sh

Have a project in mind?

Whether you need a new app, an architecture review or an extra pair of experienced hands - let's talk. I usually reply within a day.

send an emailLinkedIn ↗