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Kamil Kołodziejczyk
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Senior Frontend Developer

I rebuild legacy frontends as fast, mobile-first React apps.

Senior Frontend Developer with 8+ years in fintech, banking and logistics. Right now I'm rewriting a payment provider's merchant panel, used by several thousand merchants every day.

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One merchant panel on desktop and mobileA desktop browser window with a sidebar, a header bar and table rows, next to a phone. Both show the same form, connected by a curved line. A dimension line under both is labelled one React codebase.one React codebase
The merchant panel I'm building runs in the browser and inside the mobile app through WebView.
years of commercial frontend work
8+
industries, from banking to IoT
7
developers building on the architecture I set up
~10
merchants using my current project every day
1000s

How I work

Most of my work starts where an old system stops keeping up. I set up the new frontend from the first commit: architecture, folder structure and the standards the rest of the team builds on.

I care about code that stays easy to change a year later, so I spend time on reviews, shared components and helping junior developers find their feet. I work B2B through my own company.

Selected work

Client names stay private. The problems, the scale and my part in them are below.

Payment provider, to now

Merchant panel rewrite

Replacing a legacy PHP merchant panel with a React and TypeScript frontend built from scratch. Merchants use it every day to manage payments, so it has to stay fast and predictable.

  • Designed the architecture, folder structure and coding standards for a team of about 10
  • Built it mobile-first, so the company's mobile app embeds the same screens through WebView
  • Added data visualization modules with maps and charts
  • React
  • TypeScript
  • Redux
  • React Query
  • XState
  • Zod

Payment provider, to now

Onboarding and company verification

Multi-step onboarding where merchants verify their company (KYB) before they can accept payments. The fields and documents a merchant sees depend on the company's legal form.

  • Modelled the conditional logic so each legal form gets only the steps it needs
  • Validated API responses at the boundary to catch contract changes early
  • Built document upload with progress and error states
  • React
  • TypeScript
  • XState
  • Zod
  • React Query

Polish bank, to

Business loan application

The online application companies use to apply for a loan, inside an enterprise banking system. Delivered in a 15-person Scrum team in a regulated environment.

  • Created project skeletons and reusable component structures used across the application
  • Refined requirements directly with bank stakeholders
  • Ran internal knowledge-sharing sessions and technical trainings
  • React
  • Redux
  • TypeScript
  • .NET REST API

Transport and logistics client, to

Logistics customer portal

A customer portal built from scratch where clients price shipments, place orders and track parcels.

  • Built the quote, ordering and tracking flows end to end on the frontend
  • Contributed to frontend architecture decisions across three client projects
  • React
  • Redux
  • Java Spring REST API

Career

  1. to now

    Senior Frontend Developer

    Fintech, payment provider

  2. to

    Senior Frontend Developer

    Banking, senior from 2023

  3. to

    Frontend Developer

    Software house, logistics and enterprise clients

  4. to

    Fullstack Developer

    React frontend and Java Spring backend

  5. to

    Junior Frontend Developer

    Business apps for international clients

Stack

Frontend

  • React
  • TypeScript
  • JavaScript
  • Next.js
  • HTML
  • CSS
  • SCSS

State and data

  • Redux Toolkit
  • React Query
  • XState
  • Zod
  • GraphQL
  • REST
  • WebSockets

UI

  • Material UI
  • Ant Design
  • Styled Components
  • Storybook
  • Chart.js

Testing

  • Jest
  • React Testing Library
  • Cypress

Tooling

  • Vite
  • Webpack
  • Git
  • Docker
  • Figma
  • Azure DevOps
  • CI/CD

Domains

  • Fintech
  • Banking
  • Logistics
  • E-commerce
  • VoD
  • IoT
  • Public sector

Contact

Have a frontend project or a senior role in mind? Write to me and I'll get back to you within a couple of days.

Prefer email? Write to kontakt@kamilkolodziejczyk.dev. You can also find me on LinkedIn. My CV is available on request.