Karol Chrobok

One of 3–4 frontend developers on a client’s greenfield, multi-tenant international rental marketplace running on subscriptions — and the owner of its registration and subscription funnel, payments and CRO. Joined as a junior with no React or Next.js experience and grew into that ownership over three years.

• ~52 A/B experiments in GrowthBook across the registration and subscription funnel — building the variants defined with product and business, shipping winners as defaults, removing losing-experiment code.
• ~60 language-market locales with Lingui and Crowdin, including full RTL for Arabic and Hebrew, plus new market rollouts in DE, AU and CA.
• 7 legacy country platforms (DK, NL, GR, BE, IT, CZ, FI) migrated to the new product via 301s and canonicalisation, preserving organic traffic.
• 3 payment providers — Rebilly framepay, Apple Pay and PayPal — behind an end-to-end subscription flow: checkout, cancellation, reactivation, invoices and dashboard.

The role before the framework — layout, CSS and browser debugging built by hand, from Photoshop designs, with nothing generating the markup.

• The complete visual layer of bezuzyteczna.pl, a well-known Polish content portal — cut from PSD and wired to the site’s logic and API. Still running unchanged in production six years later.
• Client sites built and maintained end to end in semantic HTML, Sass and JavaScript — reported symptom reproduced in the browser, traced to root cause, fixed.