ZYDEV.PL
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SENIOR FRONTEND · B2B · AVAILABLE ASAP

I MAKE
SLOW APPS
FAST.

Damian Żygadło — 5+ years of React, TypeScript and Next.js across travel, e-commerce, iGaming and enterprise tooling. Every number on this page was measured before and after.

Bundle sizeWAKACJE.PL · 2026
1.8 MB500 KB−72%
LET'S TALKDOWNLOAD CV
Damian Żygadło
5 JUNIORS
HIRED

The receipts

five years · four companies · measured both ends

Bundle size

WAKACJE.PL · 2026
1.8 MB500 KB−72%

Duplicate design-system packages removed, Node dependencies deduplicated, promotions dictionary moved to SSR.

Time to interactive

CRUSTLAB · 2024
7 s2 s−71%

Iframe-embedded provider UI rebuilt as native React components. Measured in PageSpeed Insights.

Core SAP task time

FUJITSU · 2022
legacy flow3× faster−70%

Time-to-complete in the rewrite PoC — the number that unlocked funding for full scope.

Monthly visitors

BLUE OWL · 2021
125,853150,000+19%

Content and blog surface I proposed and shipped for a client store on Gatsby and WordPress.

−44%First contentful paint1.6 s → 0.9 s · Wakacje.pl
+62%E2E tests passing63 → 102 of 108 · Wakacje.pl
−55%Cold build time180 s → 80 s · Wakacje.pl
−38%Daily Sentry incidents~800 → ~500 · Wakacje.pl

Case studies

click any row for the full process
  1. WAKACJE.PL2026 — NOW

    Performance, release reliability and accessibility on Poland's largest holiday marketplace.

    • −72% bundle
    • −44% FCP
    • −55% builds
  2. CRUSTLAB2024

    Reverse-engineering, vendor negotiation and a rebuilt game surface — no downtime.

    • −71% TTI
    • new API client
  3. FUJITSU2022 — 2024

    Stack selection, domain architecture and the PoC that won the budget.

    • −70% task time
    • team lead of 3
  4. BLUE OWL2020 — 2022

    A content surface nobody asked for, pitched to the client and shipped end to end.

    • +19% visitors
    • headless WP
Wakacje.plFeb 2026 — now

Halving a travel platform's bundle without freezing feature work

Senior Frontend Developer on Poland's largest holiday marketplace — performance, release reliability and accessibility, alongside continuous feature delivery.

WHAT I WALKED INTO

  • The client bundle had grown to 1.8 MB: two copies of the internal design system shipped together with duplicated Node dependencies.
  • The full promotions dictionary was serialised to the browser on every page load.
  • Roughly 1.5% of requests failed on network errors and 5xx with no retry path — the E2E suite sat at 63 of 108 and Sentry logged ~800 incidents a day.
  • Version skew between deploys broke 10–15% of monthly releases, and a Sentry/webpack race cost 2–3 testing days every cycle.
  • Search popups trapped focus and announced nothing to screen readers.

WHAT I DID

  • Audited the bundle package by package, removed the duplicated design-system copies and deduplicated Node dependencies across workspaces.
  • Moved the promotions dictionary behind SSR so it never reaches the client.
  • Designed and shipped a request-retry layer with backoff for network and 5xx failures, then reran the E2E suite as the acceptance gate.
  • Traced the release failures to version skew and introduced version pinning between build and runtime; isolated and fixed the Sentry/webpack race.
  • Migrated Babel preprocessing to the Next.js compiler and measured cold and warm builds before and after.
  • Rewrote focus handling and aria labelling in search popups, and led the above-the-fold A/B redesign on the internal design system.

WHAT CHANGED

−72%
Bundle: 1.8 MB → 500 KB
−44%
FCP: 1.6 s → 0.9 s
+62%
E2E: 63 → 102 of 108
−38%
Sentry: ~800 → ~500 daily
−55%
Cold build: 180 s → 80 s
−36%
Warm build time

Next.js · React · TypeScript · React Query · MobX · Vitest · styled-components · Lighthouse CLI

CrustlabMar — Nov 2024

Migrating an iGaming platform off an undocumented provider

Senior Frontend Developer on a legacy casino product, brought in to take ownership of a third-party integration nobody could explain.

WHAT I WALKED INTO

  • The incumbent game provider integration had no documentation and no internal owner — only legacy code and live traffic.
  • Provider UI was embedded in iframes, pushing time-to-interactive to 7 seconds on the main game surface.
  • Login and registration were missing entirely from the new front end.
  • The vendor switch had a fixed commercial deadline and could not take the product offline.

WHAT I DID

  • Reverse-engineered the existing integration by tracing production network traffic against the legacy codebase, and documented the real contract.
  • Turned that document into the technical specification used to negotiate scope with the incoming provider.
  • Designed the replacement API client together with the new vendor's engineers, then implemented it behind a swappable interface.
  • Replaced the iframe-embedded provider UI with native React components and measured TTI in PageSpeed Insights before and after.
  • Built login and registration UIs and their API integrations from scratch.

WHAT CHANGED

−71%
TTI: 7 s → 2 s
0
Downtime during the provider switch
100%
Provider contract documented

Next.js · React · TypeScript · React Query · styled-components · PageSpeed Insights

FujitsuMay 2022 — Feb 2024

Leading three developers into a from-scratch SAP dashboard

Senior Frontend Developer and frontend lead of a 3-person team building an internal SAP administration dashboard from zero.

WHAT I WALKED INTO

  • SAP administrators completed core tasks through long multi-screen legacy flows with heavy manual steps.
  • There was no frontend architecture, no conventions and no shared component vocabulary to build on.
  • Stakeholders wanted evidence before funding a full rewrite.
  • Requirements arrived incomplete and contradictory between backend and product.

WHAT I DID

  • Selected the tech stack and defined the domain architecture, folder conventions and review standards the team worked to.
  • Produced wireframes and Material UI specifications for the core administration flows.
  • Built the proof of concept around the three highest-frequency tasks and instrumented time-to-complete against the legacy flow.
  • Ran requirement refinement sessions with backend and product, and converted the outcomes into tickets for the team.
  • Led day-to-day work for three developers: task breakdown, code review and technical decisions.

WHAT CHANGED

−70%
Time-to-complete on core SAP tasks
Approved
PoC unlocked full project scope
3
Developers led end to end

React · TypeScript · SCSS · Material UI

Blue Owl2020 — 2022

Turning a paid-traffic store into an organic one

Frontend Developer building e-commerce sites for agency clients, working directly with stakeholders from requirements to launch.

WHAT I WALKED INTO

  • A client store depended almost entirely on paid traffic, with monthly visitors flat at 125,853.
  • The site had no content surface, so it ranked for nothing beyond product pages.
  • Editors had no way to publish without a developer.

WHAT I DID

  • Proposed the blog and content section to the client myself, with the SEO and traffic case behind it.
  • Built it on Gatsby and GraphQL with WordPress as a headless CMS, so editors publish without engineering.
  • Structured templates, metadata and internal linking around product categories.
  • Handed over documentation and trained the client's team on publishing.

WHAT CHANGED

+19%
Monthly visitors: 125,853 → ~150,000
Organic
New entry pages beyond product listings
0
Developer time per published article

Gatsby · GraphQL · WordPress · JavaScript · jQuery

BEWEBDEV.TECH - CO-FOUNDER

JUN 2022 — JAN 2024

Co-hosted the @bewebdev YouTube channel and owned the Code Review series: reading real junior codebases on camera and showing how a senior reasons about them. Mentoring continues in two Discord communities — five juniors into their first frontend role.

15,000+
SERIES VIEWS
23
VIDEOS
50,000+
LIFETIME VISITS
The Code Review series on the @bewebdev YouTube channel
AVAILABLE NOW · B2B

GOT A SLOW
FRONTEND? TALK TO ME.

Kętrzyn, PL and open to relocation. Send the repo, the Lighthouse report, or just the symptom — I'll tell you what I'd measure first.

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