Articles

Articles for developers, by developers

Technical insights from building React and React Native production-grade apps, contributing to core libraries, and solving complex cross-platform challenges.

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AI
7/30/2026

3 Minutes With an Agent, 9 Seconds on Replay

Agent-device v0.20 turns known mobile journeys into scripts that agents can replay in seconds without further model calls. This article reports the experiments behind that workflow, based on 20 repeated runs, 38 Maestro flows, and 36 repair trials. It maps out when a task calls for settled observations, deterministic replay, live execution, repair, or a full re-recording as an app changes. It also covers how to validate repaired flows, prevent plausible but incorrect actions, and measure performance under realistic load.

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Michał Pierzchala

Principal Engineer

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Callstack

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AI
7/22/2026

Building Vault: A Dual-Screen Terminal for Self-Hosted AI Agents

Vault is a dual-screen handheld terminal for controlling AI agents and locally hosted LLMs from a purpose-built device. This article explains how the prototype combines an ESP32-S3, OLED, and e-paper display with an OpenClaw agent and gpt-oss-120b served on a LAN host through TensorRT-LLM. It covers the interface architecture that separates live task status from completed output, the Python broker that keeps inference off the device, the hardware failures that shaped the build, and the security limits of remote command execution.

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Lech Kalinowski

Senior AI System Engineer

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Callstack

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Super Apps
7/21/2026

A Step-By-Step Guide to Super App Development With Re.Pack 5

This hands-on guide shows how to turn two React Native applications into a minimal super app. Configure Re.Pack 5 and Module Federation, expose a mini app, register it in a host, and load it with React.lazy while handling loading and error states.

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Nazar Sydiaha

Software Engineer

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Callstack

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AI
7/20/2026

An AI Agent for Measured React Native Performance Fixes

React Native performance work can produce misleading results when teams rely on a single profiler run. This article introduces Metrognome, an open-source AI plugin that turns proposed fixes into repeated, gated experiments on a live app. It explains how the tool combines device control, render analysis, runtime signals, and performance guidance, shares examples from Uphold, and shows how its Performance Map and CI workflows prioritize issues and create evidence-backed PRs.

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Xavier Costa

Frontend Engineer

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Uphold

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Brownfield
7/8/2026

How we made Hybrid iOS apps compile 39% faster with React Native Brownfield

React Native Brownfield 3.10 brings iOS prebuilts into the packaging flow, removing a major compile step from hybrid app builds. This article explains how the integration works, what changed under the hood, and what our benchmark results show for React Native and Expo projects.

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Artur Morys-Magiera

Software Engineer

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Callstack

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Testing
7/6/2026

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

Sniffler helps JavaScript and TypeScript teams run only the E2E tests affected by a change. It traces import and export relationships and reduces unnecessary CI work without asking teams to give up test coverage.

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Szymon Chmal

Software Developer

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Callstack

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Super Apps
7/2/2026

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

This article explains what Module Federation means in React Native and how Re.Pack brings runtime-loaded JavaScript modules to mobile apps. It shows where this architecture can help, where packages or code splitting are the better choice, and what teams need to validate before adopting it in production.

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Szymon Chmal

Software Developer

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Callstack

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React Native
6/29/2026

Less Boilerplate, More Type Safety: React Navigation 8's Typed Hooks

React Navigation 8 makes typed hooks much more useful in day-to-day TypeScript work. Passing a screen name to useRoute, useNavigation, or useNavigationState gives you more specific types, cleaner route.params, and fewer unsafe casts or bulky composite types. This article breaks down what changed and where the improvements pay off most.

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Satyajit Sahoo

Software Engineer

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Callstack

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AI
6/26/2026

How Expensify Uses Agent-Device for Mobile Bug Evidence and Profiling

This article shows how we use agent-device with the Expensify app across three everyday mobile workflows: verifying bug fixes with recorded before/after evidence, measuring Sentry performance spans, and profiling React renders.

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Kacper Mikołajczak

Software Developer

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Callstack

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React
6/24/2026

Writing Custom Renderers for React

React Test Renderer’s deprecation forced React Native Testing Library to find a long-term replacement. In this article, Maciej Jastrzębski explains what it took to build a new JavaScript-only test renderer for RNTL and uses that process to show how React renderers actually work. It’s a practical look at React elements, Fiber, host instances, HostConfig, and React Reconciler for anyone who wants a clearer mental model of how JSX becomes UI.

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Maciej Jastrzębski

Software Engineer

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Callstack

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AI
6/19/2026

Building Mobile QA Agents With Vercel Eve

This article walks through migrating a mobile QA agent from a single AI SDK tool loop to Vercel Eve. It shows how Eve’s filesystem-first structure, typed tools, and durable sessions make agent behavior easier to inspect, review, and maintain inside EAS Workflows.

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Michał Pierzchala

Principal Engineer

@

Callstack

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Article
7/30/2026

3 Minutes With an Agent, 9 Seconds on Replay

See how agent-device replay cuts repeated mobile QA flows from minutes to seconds, reduces model calls, and shows when repair is worth the cost.
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Article
7/22/2026

Building Vault: A Dual-Screen Terminal for Self-Hosted AI Agents

See how Vault uses an ESP32, OLED, and e-paper display to control an OpenClaw agent and a locally served LLM on a DGX Spark.
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Article
7/21/2026

A Step-By-Step Guide to Super App Development With Re.Pack 5

Learn how to connect a React Native host and mini app with Re.Pack 5 and Module Federation, then load the remote module at runtime.
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Article
7/20/2026

An AI Agent for Measured React Native Performance Fixes

See how Metrognome combines Callstack tools for device control, render analysis, and guidance with repeated measurements to validate React Native fixes.
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Article
7/8/2026

How we made Hybrid iOS apps compile 39% faster with React Native Brownfield

See how React Native Brownfield uses iOS prebuilts to cut packaging times by up to 39% for hybrid apps, with details on setup, internals, and benchmark results.
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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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Live Stream
Live Stream
7/30/2026

How We Built a React Native News Agent With Eve

See how we built and deployed an Eve agent that tracks React and React Native repositories, filters commit noise, and publishes daily Slack updates.
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Webinar
Webinar
7/21/2026

Behavior Review for AI-Native Delivery

AI can increase code output faster than teams can verify the real app. See why behavior review matters before merge.
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Live Stream
Live Stream
7/16/2026

How to Teach Your Own AI Model, Part 2: What Should You Build First?

Explore practical AI model training, from choosing a first project and preparing data to fine-tuning locally and evaluating synthetic data.
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Podcast
7/8/2026

React Native Ease: Platform-Native Animations Without the Extra Work

Łukasz talks with Janic from App & Flow about React Native Ease, Core Animation, Reanimated trade-offs, and performant UI animation in React Native.
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Podcast
7/7/2026

What AI Changes for Paywalls and Monetization

Perttu Lähteenlahti (RevenueCat) talks about AI-generated paywalls, MCP tooling, monetization experiments, and what RevenueCat is building next across mobile and web.
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Podcast
7/7/2026

Where Reanimated Goes Next

A conversation with Bartłomiej Błoniarz on CSS animations in Reanimated, native primitives on iOS, shared element transitions, and the work still left on stability.
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Tutorial
March 19, 2026

The Hard Way vs. The React Native AI SDK Way: Stop Writing Custom Modules for Every Model

Learn how React Native AI uses a unified provider model to switch between cloud and on-device LLMs without rewriting application logic, enabling reliable AI experiences online and offline.
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Tutorial
March 12, 2026

Build Smarter Apps: Tool Calling & AI Orchestration Explained

Learn how on-device models in React Native can call tools, interact with external APIs, and return structured outputs you can use directly in application logic.
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Tutorial
March 5, 2026

MLC LLM + React Native: On-Device AI Without the Pain

Learn how to run third-party on-device LLMs in React Native using MLC LLM. Choose your models, run them efficiently across platforms, and keep a unified JavaScript API with React Native AI.
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Tutorial
February 24, 2026

Intelligent Fallbacks with Apple Intelligence in React Native

Learn how to use Apple’s built-in Foundation Models in React Native apps, reduce memory usage, and enable fast, fully on-device AI with React Native AI Apple.
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Tutorial
February 10, 2026

What Is the React Native AI SDK? A Complete Intro & Quickstart

Learn why on-device AI matters for React Native apps, how local LLMs behave offline, and what problems React Native AI is designed to solve from day one.
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Tutorial
January 29, 2026

Implementing an Android TurboModule with Kotlin

Learn how to implement a React Native TurboModule on Android, from the TypeScript spec and Codegen to the Kotlin implementation and package registration.
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Tutorial
January 19, 2026

Working with Different Threads in Swift TurboModules

Learn how JavaScript, native module, background, and main threads interact in React Native TurboModules, and how to use GCD queues to run async work safely in Swift.
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Tutorial
January 9, 2026

How to Add Type-Safe Constants to Swift TurboModules

Learn how to expose typed, immutable constants from a Swift TurboModule using Codegen, and get full end-to-end type safety between native and JavaScript.
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Tutorial
December 30, 2025

Adding Event Emitters to Your TurboModule in Swift

Learn how to emit native events from a Swift TurboModule and subscribe to them in JavaScript, including proper memory management and Codegen integration.
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Tutorial
December 22, 2025

Writing Your First TurboModule in Swift

Learn how to build a fully working TurboModule in Swift, integrate it with Codegen, and bridge it through Objective‑C inside an Expo app.