MATEUSZ
GOSZCZYCKI
Fullstack Engineer
I build
REAL-TIME SYSTEMS_
I take problems, not tickets.
Full-stack engineer from Łowicz, Poland. Self-taught, shipping production systems solo — from database schema and API to the interface and the server it runs on.
Pick a project
My journey
From the first lines of code to complete digital products — designed, built, shipped and run end to end.
// a new career, committed
const goal = 'ship real things';
while (curious) {
learn();
build();
}Six years in a kitchen
Before code there was service — long shifts that taught me to deliver under pressure, stay clean in chaos and finish on time. That discipline became the foundation for everything I build now.
export function Profile({ user }: { user: User }) {
const [open, setOpen] = useState(false);
return (
<Card onClick={() => setOpen((v) => !v)}>
<Avatar src={user.avatar} />
{open && <Details user={user} />}
</Card>
);
}Self-taught, from the markup up
Nights and weekends: HTML and CSS, then JavaScript and TypeScript, then React and modern component UIs. No bootcamp — just real projects, shipped one after another.
@Post('bids')
async placeBid(@Body() dto: BidDto) {
return this.prisma.$transaction(async (tx) => {
const top = await tx.bid.highest(dto.auctionId);
if (dto.amount <= top) throw new Conflict('outbid');
return tx.bid.create({ data: dto });
});
}Down to the database
The interface was never enough. I went deep on the backend — Node and Express, then NestJS: REST APIs, auth, SQL and NoSQL. Schema → API → UI → deploy, owned in a single pass.
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autosell.pl — first paying client
A commercial automotive marketplace, delivered solo and live in production. 30+ search filters that rank by relevance, real-time buyer–seller chat, payments and a Dockerized deploy. Requirements to prod, all mine.
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Matchdays — high-concurrency auctions
A real-time auction platform built under investor NDA: sub-100ms WebSocket bidding, atomic Prisma transactions that never lose a bid, Stripe Connect payouts and Gemini AI verification on background queues.
Complete products, owned end to end
Three production systems shipped solo — schema and API to UI, deployment and iteration. Even a fully interactive browser-based Windows XP with a custom window manager built from scratch. Every architectural decision mine.
Let's build something
Mid-level full-stack — remote, open to relocation. Give me a problem and I'll hand you a working product: architecture, backend, interface and the server it runs on.
Built and deployed a production automotive marketplace for a paying client, live at autosell.pl and used by real users.
- Delivered the full system end-to-end as a sole developer
- Built a search system with 30+ filters that ranks listings by relevance, not just date
- Implemented real-time messaging between buyers and sellers, with message history and read receipts
- Integrated TPay payment gateway for listing fees
- Implemented authentication and basic security features for production use
- Wrote integration tests with Jest and Supertest covering search filters, auth, and input validation
- Deployed to production using Docker on a Linux VPS
A professional-grade auction marketplace for sports memorabilia, engineered to handle high-concurrency bidding wars. Built with a focus on data integrity, real-time synchronization, and automated trust systems.
- Engineered a high-performance Real-Time Bidding Engine using WebSockets, achieving sub-100ms latency for price updates across all connected clients
- Implemented a bulletproof concurrency model using Prisma Atomic Transactions to prevent race conditions during simultaneous high-frequency bids
- Integrated an AI-powered verification layer using Google Gemini Vision to automatically analyze and flag suspicious or low-quality memorabilia listings
- Architected a complex multi-party payment flow with Stripe Connect, handling automated seller onboarding, escrow-like hold periods, and instant payouts
- Built a robust background processing system using Redis and Bull queues to handle heavy tasks like AI analysis and automated auction closings without impacting API performance
An incredibly complex, interactive simulation of the Windows XP operating system built entirely in the browser. A deep dive into advanced DOM manipulation, custom window management, and native HTML5 APIs.
- Engineered a custom Window Management system from scratch, handling complex drag-and-drop bounding, z-index stacking algorithms, and minimize/maximize states
- Recreated functional legacy applications, including a fully operational Winamp player using the HTML5 Audio API and a retro Gadu-Gadu messenger
- Developed a deeply nested, globally synchronized state architecture linking the taskbar, system tray, desktop icons, and active window processes
- Built a highly authentic boot sequence and custom 'Glitch/Blue Screen' engine using advanced CSS animations and React lifecycles
- Implemented a functional File Explorer routing system to showcase portfolio projects within the retro OS environment
The site you're looking at — a motion-driven developer portfolio. A scroll-told journey, animated 3D/ASCII backgrounds, an interactive project deck and a built-in code viewer. Pure frontend and motion craft, owned end to end.
- Built a scroll-driven 'My Journey' as one continuous, guided timeline animation
- Designed an interactive project deck with 3D flip cards and a built-in VS Code-style code viewer
- Engineered a custom animated cursor, an ASCII intro loader and scramble/typewriter text effects
- Statically generated with the Next.js App Router, React 19 and strict TypeScript
Let's build
something.
Open to mid-level full-stack roles and ambitious projects. Give me a problem — I'll own it from architecture to the server it runs on. Remote-first, CET.
❯ status --contact
© 2026 Mateusz Goszczycki · Built from scratch
Working globally · CET