Jonatan Witoszek

Senior Software Engineer

Software engineer with 7+ years of experience building production web applications in React and TypeScript. I own complex product work end-to-end, from shaping abstractions and shipping user-facing workflows to improving observability, reliability, and production operations. My work spans large SPAs, integration-heavy systems, and internal tooling, with a focus on making products easier to ship, run, and support.

View CV ->

Skills

Languages

TypeScriptJavaScriptPythonGraphQLHTML/CSS

Frontend

ReactNext.jsTailwind CSSDesign SystemsStorybookshadcn/uiAccessibilityJotai

Backend & APIs

Node.jsGraphQLDjangotRPCREST APIsWebhooksDynamoDB

Payment Systems

AdyenTransaction APISplit PaymentsWebhook ArchitectureApple Pay / Google Pay

Observability

OpenTelemetryDatadog

Testing

PlaywrightVitestJestReact Testing LibraryAccessibility Testing

Tools & DevOps

DockerTerraformMonorepospnpmESLintViteGitHub ActionsVercelAWS Lambda

Architecture & Security

RFC authoringSupply chain securityGraphQL schema designDistributed systemsMulti-tenant architecture

Experience

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Saleor

Senior Software Engineer & Open Source Maintainer

Feb 2022 — Present

Open Source Ecommerce Platform

Payment App (Adyen)

Adyen payment app for Saleor’s app-based architecture, where Saleor manages the transaction layer and the app integrates with Adyen

Evolved the Adyen app from early prototype to a production-grade integration used by key merchants, supporting complex provider workflows such as 3D Secure, split payments, Apple Pay, stored payment methods, captures, refunds, and cancellations.
Improved reliability of event-driven payment flows through reconciliation logic, idempotency safeguards, and DynamoDB-backed storage for tenant configuration, transaction state, and expiring operational logs in a multi-tenant serverless environment.

TypeScriptNext.jstRPCJSON SchemaOpenTelemetryDynamoDBDatadogPlaywrightPolly.jsBruno

Saleor Dashboard

SPA admin panel for managing online stores powered by Saleor

Led rollout of Saleor’s new Transaction API experience in the Dashboard, including split payments, payment balance views, refund approval and execution workflows, manual capture, and feature-flagged migration from the legacy payments model.
Re-architected filtering in a large React/TypeScript SPA into reusable abstractions, improving reliability and consistency across Products, Orders, Customers, and modal workflows.

TypeScriptReactGraphQLApollo Clientreact-routerPlaywright

App SDK & Developer Experience

TypeScript SDK and tooling for building Saleor apps across frameworks and runtimes

Rewrote App SDK from a Next.js-centric library into a universal, platform-agnostic toolkit by introducing reusable runtime abstractions and removing legacy middleware.
Added first-class support for Web API runtimes (Cloudflare, Deno, etc.) and AWS Lambda, enabling Saleor apps to run outside Vercel in serverless and edge environments.

TypeScriptNode.jsAWS LambdaCloudflare WorkersDynamoDBZodGitHub Actions

Platform Infrastructure & Identity

Internal platform work spanning monitoring infrastructure and authentication experience

Migrated Datadog dashboards and alerts to Terraform, moving monitoring into version-controlled infrastructure as code.
Improved operational reliability by auditing monitors, reducing alert noise, and strengthening logging around app installation and production issues.

TerraformDatadogKeycloakHelmReactTypeScript

Ecosystem Tooling & DX

Reusable templates, linting, and developer tooling for Saleor apps and the broader ecosystem

Helped create Saleor’s payment app template, establishing configuration, validation, and testing patterns reused across future payment integrations.
Built reusable ESLint tooling for Saleor apps, including a recommended config and custom validation rules that improved consistency across integrations.

TypeScriptESLint (plugins)tRPCHonoCloudflareDenoGitHub Actions

Macaw UI

Saleor's design system and component library, used across Dashboard, Cloud, Checkout, and other product surfaces

Expanded Saleor’s design system with reusable components such as Chip, Avatar, Tooltip, and Pill, improving UI consistency across multiple products.
Introduced framework-agnostic navigation patterns for shared components like IconButton, Backlink, Sidebar, and Pagination, enabling custom Link integrations and better power-user workflows such as opening views in new tabs.

TypeScriptReactRadix UIvanilla-extractStorybook

Netguru

Front-end Developer

May 2021 — Feb 2022

Software House

CRM Web App

CRM application for a company in the renewables & environment sector

Automated Pull Request flow using danger.js in CI pipeline, decreasing code review time.
Improved Core Web Vitals by optimizing large images with modern formats (WebP, AVIF).

TypeScriptReactReduxRxJSSocket.ioMaterial UIstyled-components