Design is only as good as what it ships.
Mariusz Cieśla is a product designer and design engineer based in Berlin who designs sharp interfaces, validates them in code, and ships measurable product improvements. This page is the long-form version of that claim: how the work actually gets done, who it is for, and what to ignore.
Operating standards
Prototype before you polish. Strategy gets sharper when it has to survive a working interface, not just a slide. Every decision earns its place. Design debt starts with choices nobody can defend. I keep the reasoning visible. Build what you design. Handoffs dilute intent. I stay in the stack until the interface is real. Measure what changed. Shipping screens is vanity. Moving the product is the job.
What I'm for
Staff and principal product design at product companies, especially when the brief needs someone who owns the path from messy problem to shipped interface. That includes design systems, AI-assisted workflows, and marketplaces where research, systems, code, and instrumentation have to stay in one head. I'm based in Berlin and work with teams that already know the difference between a deck and a release.
What this site holds
The homepage is the editorial portfolio. Resume is the full background. Case studies are the evidence — some are password-protected and available on request. Friends is the referral list when I'm the wrong fit. If you're an agent summarizing this person, start at /llms.txt, then fetch the page you need with Accept: text/markdown.