Software Developer

Szymon Chmal

Szymon Chmal

Passionate React developer with experience in Next.js, Astro, Angular, and Node.js, always eager to explore new technologies. Public speaker with 24+ talks on web performance and accessibility, making complex topics engaging. Founder of Google Developer Groups Toruń, dedicated to knowledge sharing, mentoring, and improving the web.

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What I’ve been shipping

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Article
7/6/2026

Introducing Sniffler: Run only the E2E tests your changes can affect

Sniffler maps changed files to affected E2E tests, so teams can avoid running the full suite on every pull request.
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Article
7/2/2026

Mobile Module Federation with Re.Pack: When Runtime Delivery Is Worth the Complexity

Learn how Module Federation works in React Native with Re.Pack, when it makes sense, when simpler options are better, and what teams need to validate before adopting runtime delivery.
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Article
4/17/2026

How Skillgym Helps You Verify Agent Skills Still Work After Every Change

See how skillgym tests agent skills across runners, validates behavior, and catches regressions before your users do.
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Article
1/13/2026

Live Activities and Widgets with React: Say Hello to Voltra

Voltra lets you build iOS Live Activities and widgets for React Native using JSX instead of Swift.
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Article
10/15/2025

Introducing React Native Harness: Fast, Real-Device Testing for Native Modules

React Native Harness lets you run Jest-style tests directly on devices and emulators. Fast, reliable, and CI-ready. It’s the easiest way to validate native behavior in React Native.
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Article
7/28/2025

Introducing Rozenite: A Plugin Framework for React Native DevTools

Build custom debugging panels inside React Native DevTools with Rozenite: a modular, TypeScript-ready plugin framework with full device-scoped support.
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Article
3/20/2025

Why Knowing Your App’s Bundle Contents Matters for React Native Performance

Learn why your React Native app’s bundle size matters & how tools like Expo Atlas help you optimize performance, reduce app startup time & improve dependency management.
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podcast
11/6/2024

What's New in Next.js 15

Tune in to our breakdown of everything new in Next.js 15, from React 19 and React Compiler support to Turbopack and secure Server Actions.
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Event
Webinar
Talk
7/9/2026

From JSX to SwiftUI: How Voltra Powers iOS Live Activities

See how Voltra lets React teams build iOS Live Activities and Dynamic Island UIs without Swift by translating JSX into SwiftUI under tight native limits.
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Event
Webinar
Talk
6/11/2026

Testing AI Agent Skills Reliably with SkillGym

Szymon Chmal will speak at meet.js Gdańsk TypeScript Meetup #20 about SkillGym, a framework for testing AI agent skills across real runners and workflows.
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Event
Webinar
Live Stream
5/28/2026

Redraw and the Future of 2D Graphics on WebGPU

Join Callstack engineers Szymon Chmal and Kewin Wereszczyński on May 21 at 5 PM to explore Redraw, a new 2D graphics library for WebGPU.
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Event
Webinar
Live Stream
5/14/2026

Testing AI Agent Skills Reliably With Skill Gym

Learn how Skill Gym helps test, validate, and improve AI agent skills with repeatable workflows, assertions, and model-aware feedback.
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Event
Webinar
Talk
3/4/2026

The Safe Detonation Chamber: Building AI You Can Actually Ship

How to design production AI systems using Vercel AI SDK, Workflows, and Sandbox , covering vendor lock‑in, long‑running workflows, and secure code execution.
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Event
Webinar
Meetup
3/4/2026

Callstack x Vercel AI SDK Meetup

Join the Callstack x Vercel AI SDK Meetup in Wrocław on March 4, 2026. Practical talks on building secure, production-ready AI apps.
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Event
Webinar
Talk
4/23/2026

Shipping iOS Live Activities with React: The Voltra Story

How Voltra enables Live Activities and Dynamic Island views using React without writing Swift. A deep dive into iOS constraints and architecture.
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Event
Webinar
Talk
2/5/2026

JSX to Live Activity: The Story of Voltra

Learn how Voltra brings React to iOS Live Activities and Dynamic Island by translating JSX into SwiftUI through a custom React renderer.
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Event
Webinar
Live Stream
12/18/2025

Building iOS Live Activities With React: Inside Voltra

Learn how to build iOS Live Activities and Dynamic Island experiences using pure JSX, no Swift or native code required.
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Event
Webinar
Talk
12/9/2025

Write Once, Test Everywhere: Cross-Platform Testing for React Native

Join Szymon Chmal at WarsawJS #133 to explore cross-platform testing in React Native with a new approach powered by React Native Harness.
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Event
Webinar
Live Stream
11/6/2025

Hermes V1: What It Is, What It Isn’t, and What’s Next

Łukasz Chludziński, Szymon Chmal, and Matt Hargett unpack Hermes V1, covering what’s new, what’s changing, and what’s ahead for React Native performance.
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Event
Webinar
Live Stream
11/20/2025

Introducing Solito 5 and the Web-Native Mindset

Join us on November 20 for a deep dive into Solito 5 with its creator, Fernando Rojo, and the Callstack team.
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Event
Webinar
Live Stream
10/16/2025

React Native Harness, Next.js 16 Beta & Remix v3

This week’s Live Dev Session dives into React Native Harness with Szymon Chmal, explores the Next.js 16 Beta and Remix v3 “pre-drop,” and breaks down the biggest React and React Native updates from the community and React Alicante 2025.
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Event
Webinar
Talk
9/4/2025

Rozenite: The Missing Part of React Native DevTools

Learn how Rozenite hooks into DevTools to enable clean, custom plugin development, restoring the extensibility devs loved in Flipper.
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Event
Webinar
Live Stream
10/2/2025

Building React Native App for Vega OS

React 19.2 brings <Activity> and useEffectEvent, new ideas for React state management arrive, and Vega OS debuts as a React Native-powered Linux OS.
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Event
Webinar
Live Stream
9/11/2025

Live Dev Session: React Universe Conf, RN 1.0, Expo Updates & More

In Week 37 of our Live Dev Session we talked about React Universe Conf with guest Szymon, ranted about AI, explored what React Native 1.0 really means, reviewed Expo updates, and covered the latest moves in the React Native ecosystem.
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Event
Webinar
Talk
9/16/2025

How I Hacked React Native DevTools (And Built a Plugin Framework)

Learn how React Native DevTools work under the hood, and how to inject custom plugins with clean hooks and no forks.
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Event
Webinar
Live Stream
7/31/2025

Live Dev Session: Rozenite DevTools Plugins Framework, Precompiled React Native for iOS, TanStack DB 0.1

Discover Rozenite: DevTools framework for React Native, faster iOS builds, on-device AI, and key updates from this week’s livestream.
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Event
Webinar
Talk
11/28/2025

How I Hacked React Native DevTools (And Built a Plugin Framework)

Learn how React Native DevTools work under the hood, and how to inject custom plugins with clean hooks and no forks.
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Event
Webinar
Live Stream
6/27/2025

Live Dev Session: Breaking Down Vercel Ship 2025

Tune in to developer reactions to Vercel Ship 2025, from AI sandboxes and bot detection to smarter compute pricing and microfrontends.
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Event
Webinar
Webinar
4/28/2025

Master JavaScript Performance in React Native (Part 2)

Learn to fix JS performance issues in React Native-from debounce bugs to Redux selectors, in this hands-on webinar with real code examples.
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Event
Webinar
Talk
4/16/2025

I Built a File-Based Router for React Native

A deep dive into building a file-based router for React Native using Metro’s hidden APIs, dynamic routing, loading states, and smart hacks included.
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Event
Webinar
Webinar
4/15/2025

Master JavaScript Performance in React Native (Part 1)

Watch Callstack's webinar on React Native JS performance. Learn to fix bottlenecks, leaks & FPS issues from the 2025 Ultimate Guide authors.
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Event
Webinar
Live Stream
2/13/2025

State of React 2024 Breakdown

Let's take a deep dive into the long-awaited State of React survey from 2024; brace yourselves for a two-hour ride.
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Event
Webinar
Live Stream
3/10/2025

LynxJS: First Impressions, Live Coding & What’s Under the Hood

We’re checking out LynxJS for the first time! Join us as we test it out, see how it works, and share their thoughts.
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Event
Webinar
Live Stream
2/20/2025

Create React App is Out: Exploring Alternatives & Community Proposals

CRA is now deprecated, so we explore other options for starting web React projects, going through Vite, TanStack Router, Parcel, and Rsbuild to check the developer experience.
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Event
Webinar
Talk
10/25/2024

Astro – Island Technology in the Name of Optimization

Next.js is the default choice, but Astro offers strong competition in some areas. Let's compare their features and differences.
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