Sebastian Kolbusz
Full-Stack Engineer | React & Next.js Specialist
Sebastian builds stable, high-performance web applications with 6+ years of commercial experience, combining deep frontend expertise in React and TypeScript with full-stack ownership from architecture through production deployment.
Skills
At a glance
6+
Years of commercial experience
50%
Bundle size reduction (Ready2order)
99.9%
Application uptime maintained
9+
Years freelance practice
Experience
Full-Stack Engineer
Ready2order · 08/2019 – 12/2025
Architected and optimized a business-critical SaaS POS application, reducing production bundle sizes by 50% through aggressive code splitting and strategic state management refactoring. Drove design system evolution across three major iterations (Styled-components → Tailwind CSS → CSS Modules), built complex modular features using React and TypeScript with GraphQL/REST integration, and maintained 99.9% uptime for high-volume financial transactions through rigorous end-to-end and unit testing.
Freelance Developer
Self-employed · 05/2016 – Present
Takes full ownership of web applications from discovery through deployment and monitoring. Architected a zero-footprint multi-tenant content ecosystem using Astro and Payload CMS, manages complete infrastructure including VPS deployment, domain routing, SSL, and Cloudflare optimization, and builds responsive, performance-oriented web platforms for independent clients using Next.js, Vite, and TypeScript.
Projects
Multi-Tenant Content Network
Engineered a high-performance, zero-footprint ecosystem of isolated satellite web applications built with Astro, driven by a single Payload CMS instance and monitored via privacy-focused Rybbit analytics to prevent cross-site tracking.
POS Application Performance Optimization
Cut production bundle sizes by 50% through Webpack configuration rewrites, aggressive code splitting, dead code elimination, and migration from Redux to lightweight alternatives including Apollo Client cache and React Context.
Design System Migration
Led technical migration of core UI styling across major product iterations, transitioning from Styled-components to Tailwind CSS to CSS Modules to achieve deterministic style encapsulation and improved performance.
Highlights
- Operates at the intersection of software and hardware, retrofitting physical electronics and adapting firmware to bridge code and physical systems
- Enforces high technical standards through rigorous code reviews, comprehensive testing suites (Cypress, Jest, Playwright), and systematic technical debt minimization
- Thrives in autonomous, high-trust environments focused on delivering fully debugged, production-ready solutions