---
title: "Maciej Jastrzębski"
description: "Maciej Jastrzębski maintains React Native Testing Library and Reassure, and builds native iOS and Android products. Meet the Callstack engineering team."
url: https://www.callstack.com/team/maciej-jastrzebski
updated: 2026-10-22T14:18:28.042Z
---

# Maciej Jastrzębski

Maciej Jastrzębski maintains React Native Testing Library and Reassure, and builds native iOS and Android products. Meet the Callstack engineering team.

_Software Engineer_

An expert in building native iOS and Android apps with years of experience. Passionate about creating well-architected, high-quality mobile applications and enabling dev teams to work efficiently. Maintainer of React Native Testing Library and Reassure OSS projects, with a strong focus on TypeScript, best practices, new architecture, testing, and performance. Enjoys traveling and capturing travel photography.

[LinkedIn](https://www.linkedin.com/in/mdjastrzebski/) · [X](https://twitter.com/mdj_dev) · [GitHub](https://github.com/mdjastrzebski)

## What I’ve been shipping

- [Writing Custom Renderers for React](https://www.callstack.com/blog/writing-custom-renderers-for-react) (Article, 6/24/2026): Learn how React renderers work, why RNTL needed a new test renderer, and what it takes to connect React Reconciler to a host environment.
- [Scaling React Native at Zalando: How Brownfield Migration Paid Off](https://www.callstack.com/events/scaling-react-native-at-zalando-lessons-from-brownfield-migration) (Webinar, 11/5/2025): Discover how Zalando scaled React Native across a massive e-commerce app, from internal buy-in to brownfield rollout, and what they learned.
- [Adding React Native to an Existing Flutter App](https://www.callstack.com/blog/adding-react-native-to-an-existing-flutter-app) (Article, 7/24/2024): Discover how to integrate React Native into an existing Flutter app, leveraging platform views and setting up on both Android and iOS.
- [What's New in Reassure 1.0](https://www.callstack.com/podcasts/whats-new-in-reassure-1-0) (Podcast, 7/17/2024): Find out how to monitor React and React Native performance better than ever before with Reassure's new features.
- [React Native Performance in 2024: Challenges, Solutions, Forecasts](https://www.callstack.com/podcasts/react-native-performance-in-2024-challenges-solutions-forecasts) (Podcast, 3/28/2024): Join us as we explore the latest developments in React Native performance optimization with experts from Expo and Callstack.
- [Reassure - Open Source Tool Measuring Performance Regression](https://www.callstack.com/podcasts/reassure-performance-regression-measurement-tool) (Podcast, 7/28/2022): Explore Reassure, an Open Source tool for measuring performance regression in React Native apps.
- [React Native Testing Library With Redux](https://www.callstack.com/blog/react-native-testing-library-with-redux) (Article, 8/5/2020): In this article, we discuss how Redux can be helpful in proceeding tests with React Native Testing Library and how can you benefit from this solution.

JOIN US

## Build the AI-native React Native future

Work with engineers who contribute to the ecosystem and turn new technology into real products. At Callstack, AI is part of how we build, learn, and ship software.

[Join Us](https://www.callstack.com/careers)

[About us](https://www.callstack.com/about-us)