Jonatan Witoszek

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.
• ▸ Built advanced observability with custom OpenTelemetry infrastructure and distributed tracing across Saleor, the app, and Adyen API, enabling faster investigation of webhook bottlenecks, retries, p99 outliers, and merchant-specific production issues.
• ▸ Established patterns later reused across other integrations, including DynamoDB usage, observability setup, typed webhook schemas, and integration testing workflows.

TypeScript · Next.js · tRPC · JSON Schema · OpenTelemetry · DynamoDB · Datadog · Playwright · Polly.js · Bruno

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, grant refunds, 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.
• ▸ Improved engineering workflows in the Dashboard through AI-assisted development guardrails and large-scale codebase maintenance, including deterministic Claude Code hooks and dead-code cleanup across 900+ files.
• ▸ Reworked Dashboard filtering into a reusable FilterDefinition system that unified query behavior across Products, Orders, Customers, and later generic modal flows.

TypeScript · React · GraphQL · Apollo Client · react-router · Playwright

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.
• ▸ Built working examples for AWS Lambda, Cloudflare Workers with Hono, and Deno Deploy with Hono, making the SDK easier to adopt across serverless and edge platforms.

TypeScript · Node.js · AWS Lambda · Cloudflare Workers · DynamoDB · Zod · GitHub Actions

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.
• ▸ Modernized the Saleor Cloud identity experience by replacing legacy Keycloak templates with a React-based theme built with Keycloakify and the Macaw design system.

Terraform · Datadog · Keycloak · Helm · React · TypeScript

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.

TypeScript · ESLint (plugins) · tRPC · Hono · Cloudflare · Deno · GitHub Actions

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.
• ▸ Modernized the library for newer React patterns by fixing Strict Mode and React 18 compatibility issues and improving Storybook-based development workflows.

TypeScript · React · Radix UI · vanilla-extract · Storybook

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).
• ▸ Prevented critical service worker deployment issue that would have blocked future releases.

TypeScript · React · Redux · RxJS · Socket.io · Material UI · styled-components

Modernizing a legacy web app for a mental health care business

• ▸ Conducted accessibility review and suggested ADA compliance improvements.
• ▸ Cut Webpack build time by 50%, improving developer productivity.
• ▸ Prepared tech debt elimination plan that was slowing development.

TypeScript · React · Redux · Storybook · XState · Accessibility