Architecture & Performance

Solve your hardest engineering challenges.

We help products get past technical limits that slow delivery and hurt quality. Senior engineers solve the underlying issues so teams can ship faster with more confidence.

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Trusted by 100+ Enterprise clients

Why solve it with Callstack

Fix the limits blocking delivery.

Senior engineers trace the root causes behind slow, flaky, or hard-to-ship code. We handle demanding native and architecture work without pulling your roadmap off course.

  • Improve speed and stability.

    Fix the issues that hurt user experience and release confidence.

  • Remove engineering bottlenecks.

    Solve architecture and codebase problems that slow delivery down.

  • Get the hard work done.

    Senior engineers handle demanding native and low-level work without derailing the roadmap.

  • Strengthen the foundation.

    Leave the product easier to maintain, extend, and ship from.

Services

Fix the engineering limits blocking delivery.

  • Performance

  • React Native Performance Optimization

    Profile and tune React Native apps to find the bottlenecks behind slow starts, dropped frames, and memory leaks.

  • AI Vibe Coding Cleanup

    Review and refactor code written by AI tools before it ships, where fast output often hides missing edge cases, weak patterns, and architectural shortcuts.

  • Native & Low-Level

  • React Native Modules Development

    Build custom native modules in Swift, Kotlin, and Objective-C when the JavaScript layer cannot reach the platform capability the product needs.

  • React Native Brownfield Integration

    Embed React Native inside an existing native iOS or Android app, adding new screens and features without rewriting the surrounding codebase.

  • C++ Library Integration

    Bring existing C++ libraries into React Native through JSI, giving the app access to shared cross-platform logic and performance-critical code.

  • Shared Native Core

    Build one C++ or Rust core for mobile, web, desktop, and TV so teams avoid per-platform rewrites and logic drift.

  • Custom High-Performance Renderers

    Build specialized rendering engines for graphics, media, and immersive experiences where off-the-shelf components cannot meet the performance the product needs.

Architecture & Performance

Get an architecture review.

Point us at the code that's slow, flaky, or hard to ship. Our senior engineers come back with root causes and a prioritized fix plan.

Book a call

How we work together

Turn technical limits into shipped fixes.

  • Extend your team

    Our senior engineers join your team to ship features, guide technical decisions, and strengthen delivery.

    • Your roadmap and workflow
    • Expertise shared as we work
    • Flexible timezone coverage

  • Deliver a project

    We take agreed work from technical planning to release, with clear responsibilities and progress you can see.

    • 3 Callstack engineers ship like 6
    • Impact visible before sprint two
    • End-to-end delivery

  • Solve specific challenge

    We address a performance, migration, or infrastructure challenge, or run training around your team’s needs.

    • Focused reviews or implementation
    • Knowledge your team keeps
    • Outcomes guaranteed with contract
React Foundation Founding Member
300+ commits to React Native
Industry runs on our tooling
50M+
OSS downloads / month
5x
Faster message sending time
-28%
CPU usage in critical trading flows
Our app has hundreds of features and before we switched to Re.Pack we were struggling to scale the performance. Re.Pack is built on Webpack, so it allowed us to leverage existing tooling and approaches to scale more linearly. If the default tooling isn't working for your use case, I'd recommend giving Re.Pack a try!
Mike Duminy
Principal Engineer / Klarna
100+
Enterprise projects delivered

10 years of React Native → Now in your AI stack

Get an architecture review.

Point us at the code that's slow, flaky, or hard to ship. Our senior engineers come back with root causes and a prioritized fix plan.

Book a call

Open Source

Build with our open-source tools.

We open-source the tools behind our delivery model.
Use them, fork them, or let us run them for you.

Check All ToolsExplore AI Infrastructure

Reassure

Performance testing companion for React and React Native

1.5K stars

React Native Harness

Harness brings Jest-style tests to real native environments so you can test TurboModules like you would test your React Native app: with JavaScript.

179.7K downloads/mo

Rozenite

Plug-and-play panels for React Native DevTools. Install, enable, and start debugging in minutes.

959.8K downloads/mo

Re.Pack

A webpack-based toolkit to build your React Native application with full support of webpack ecosystem

2.2M downloads/mo

React Native Sandbox

Run multiple, isolated React Native instances within a single application

15.4K downloads/mo

React Native Brownfield

Incrementally move your iOS and Android apps to React Native without breaking

552 stars

Agent Skills

Callstack’s best practices on React Native performance optimization, upgrading, CI workflows, and brownfield migrations

1.7K stars

Insights

Worth your time, by engineers.

Explore Insights
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Nov 17Talk

Efficient On-Device LLMs in React Native Done Right

Artur Morys-Magiera will cover efficient on-device LLMs in React Native, including runtimes, model selection, quantization, and platform constraints.

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Nov 17Talk

On-Device AI After WWDC: What Changed for React Native

Mike Grabowski will explain what changed for system-provided on-device AI after WWDC and what React Native developers can build with it.

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Oct 7Talk

Building a Modern Navigation Library: The Hard Parts

At reactCon, Satyajit Sahoo explores the design choices behind React Navigation 8 and the challenges of creating a navigation library that works across platforms.

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Sep 24Talk

JSX to Live Activity: The Story of Voltra

Szymon Chmal will show how Voltra brings iOS Live Activities and widgets to React Native without requiring developers to write native UI code.

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Sep 24Talk

Building a Modern Navigation Library: The Hard Parts

Satyajit Sahoo will share the decisions and trade-offs behind React Navigation 8 and building a modern cross-platform navigation library.

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Sep 7Podcast

Running AI in the Browser With Transformers.js

Nico Martin explains how Transformers.js uses WebGPU and ONNX to run AI in the browser, plus the limits of local models and on-device agents.

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Aug 4Podcast

VisionCamera V5 With Marc Rousavy

Marc Rousavy joins Mike Grabowski to unpack VisionCamera v5, Nitro Modules, the constraints API, migration work, and what changed for React Native camera apps.

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Jul 20Article

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.