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React Native Best Practices

CallstackOfficialPublished by Callstack

  • Skill
  • Guidelines
  • Software development
  • MIT
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From the author

Provides React Native performance optimization guidelines for FPS, TTI, bundle size, memory leaks, re-renders, and animations. Applies to tasks involving Hermes optimization, JS thread blocking, bridge overhead, FlashList, native modules, or debugging jank and frame drops.
— the description by Callstack

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a structured approach to optimizing React Native applications. It focuses on critical performance metrics including FPS, Time to Interactive (TTI), bundle size, and memory management. The guide emphasizes a data-driven workflow: Measure, Optimize, Re-measure, and Validate, ensuring that performance improvements are based on actual profiling data rather than assumptions. It covers both JavaScript-level optimizations and native-level configurations, providing actionable strategies for common bottlenecks like list rendering, re-renders, and heavy native modules.

What it does

  • Provides a standardized performance measurement and optimization workflow
  • Offers specific guidance for improving FPS and reducing UI re-renders
  • Details techniques for analyzing and reducing JavaScript bundle sizes
  • Outlines strategies for optimizing TTI and native module performance
  • Includes best practices for memory leak detection and management
  • Provides a mapping of common performance problems to specific diagnostic and fix strategies

When to use it

  • When debugging janky UI, frame drops, or slow animations
  • When investigating memory leaks in JS or native code
  • When optimizing app startup time and TTI
  • When attempting to reduce the final application bundle size
  • When profiling and tuning native modules or Turbo Modules
  • During code reviews to ensure performance-conscious implementation

Advantages

  • Promotes a rigorous, evidence-based approach to performance tuning
  • Covers the full stack from React components to native bridge and bundle configuration
  • Provides clear, priority-ordered guidelines for triage
  • Includes specific diagnostic commands for profiling and bundle analysis
  • Helps avoid common pitfalls like premature optimization or incorrect dependency usage

Usage examples

“My React Native app is dropping frames during list scrolling. How should I investigate?”
The agent will guide you to use the FPS and re-render profiling workflow, suggesting the use of react-devtools to identify slow components and recommending the replacement of ScrollView with optimized alternatives like FlashList.
“How can I reduce the size of my React Native iOS bundle?”
The agent will provide steps to analyze the bundle using source-map-explorer, identify heavy dependencies, and apply optimizations such as avoiding barrel imports and enabling native code shrinking.

Install

  1. 1 of its files are not mirrored here, so install it from its source:

    https://github.com/callstackincubator/agent-skills/tree/59e9d17446a248b21d86f078fcd0bd2d36db1ca4/skills/react-native-best-practices

Documentation by Callstack

React Native Best Practices

Overview

Performance optimization guide for React Native applications, covering JavaScript/React, Native (iOS/Android), and bundling optimizations. Based on Callstack's "Ultimate Guide to React Native Optimization".

When to Apply

Reference these guidelines when:

  • Debugging slow/janky UI or animations

  • Investigating memory leaks (JS or native)

  • Optimizing app startup time (TTI)

  • Reducing bundle or app size

  • Writing native modules (Turbo Modules)

  • Profiling React Native performance

  • Reviewing React Native code for performance

Security Notes

  • Treat shell commands in these references as local developer operations. Review them before running, prefer version-pinned tooling, and avoid piping remote scripts directly to a shell.

  • Treat third-party libraries and plugins as dependencies that still require normal supply-chain controls: pin versions, verify provenance, and update through your standard review process.

  • Treat remote chunk loading as first-party artifact delivery only. Prefer app-bundled chunks or signed CI release manifests; hosted chunks must come from trusted HTTPS origins you control and be pinned to the current app release.

Priority-Ordered Guidelines

PriorityCategoryImpactPrefix
1FPS & Re-rendersCRITICALjs-*
2Bundle SizeCRITICALbundle-*
3TTI OptimizationHIGHnative-*, bundle-*
4Native PerformanceHIGHnative-*
5Memory ManagementMEDIUM-HIGHjs-*, native-*
6AnimationsMEDIUMjs-*

Impact labels are triage hints: CRITICAL first, HIGH next, MEDIUM when evidence points there.

Quick Reference

Optimization Workflow

Follow this cycle for any performance issue: Measure → Optimize → Re-measure → Validate

  1. Measure: Capture baseline metrics before changes. For runtime issues, prefer commit timeline, re-render counts, slow components, heaviest-commit breakdown, and startup/TTI when available. Component tree depth or count are optional context, not substitutes. Do not recommend memoization, atomic state, or compiler changes without a measured render or FPS problem.

  2. Optimize: Apply the targeted fix from the relevant reference

  3. Re-measure: Run the same measurement to get updated metrics

  4. Validate: Confirm improvement (e.g., FPS 45→60, TTI 3.2s→1.8s, bundle 2.1MB→1.6MB)

If metrics did not improve, revert and try the next suggested fix.

Review Guardrails

  • Check library versions before suggesting API-specific fixes. Example: FlashList v2 deprecates estimatedItemSize, so do not flag it as missing there.

  • Do not suggest useMemo or useCallback dependency changes unless behavior is demonstrably incorrect or profiling shows wasted work tied to that value.

  • Do not report stale closures speculatively. Show the stale read path, a repro, or profiler evidence before calling it out.

  • When profiling a flow, measure the target interaction itself. Do not treat component tree depth or component count as the main performance evidence.

Critical: FPS & Re-renders

Profile first:

agent-device react-devtools status
agent-device react-devtools wait --connected
agent-device react-devtools profile start
agent-device react-devtools profile stop
agent-device react-devtools profile slow --limit 5
agent-device react-devtools profile rerenders --limit 5
agent-device react-devtools profile timeline --limit 20

Drive the target interaction with normal agent-device commands between profile start and profile stop.

Manual fallback when agent-device is unavailable: open React Native DevTools from Metro (j) or the Dev Menu, use the Profiler tab, and record the same interaction.

For release-build React component profiling, connect @callstack/inspector first so React DevTools can attach to the release app, then run the agent-device react-devtools flow above.

Common fixes:

  • Replace ScrollView with FlatList/FlashList/Legend List for long lists

  • After profiling shows cascading re-renders, use React Compiler for automatic memoization

  • After profiling shows broad store/context updates, use atomic state (Jotai/Zustand) to reduce re-renders

  • Use useDeferredValue for expensive computations

Critical: Bundle Size

Analyze bundle:

npx react-native bundle \
  --entry-file index.js \
  --bundle-output output.js \
  --platform ios \
  --sourcemap-output output.js.map \
  --dev false --minify true

npx source-map-explorer output.js --no-border-checks

Verify improvement after optimization:

# Record baseline size before changes
ls -lh output.js  # e.g., Before: 2.1 MB

# After applying fixes, re-bundle and compare
npx react-native bundle --entry-file index.js --bundle-output output.js \
  --platform ios --dev false --minify true
ls -lh output.js  # e.g., After: 1.6 MB  (24% reduction)

Common fixes:

  • Avoid barrel imports (import directly from source)

  • Remove unnecessary Intl polyfills only after checking Hermes API and method coverage

  • Evaluate tree shaking (Expo SDK 52+ experimental unused import/export removal, or Re.Pack only if already configured)

  • Enable R8 for Android native code shrinking

High: TTI Optimization

Measure TTI:

  • Use react-native-performance for markers

  • Only measure cold starts (exclude warm/hot/prewarm)

Common fixes:

  • For React Native 0.78 and earlier, disable Android JS bundle compression to enable Hermes mmap

  • Use native navigation (react-native-screens)

  • Preload commonly-used expensive screens before navigating to them

High: Native Performance

Profile native:

  • iOS: Xcode Instruments → Time Profiler

  • Android: Android Studio → CPU Profiler

Common fixes:

  • Use background threads for heavy native work

  • Prefer async over sync Turbo Module methods

  • Use C++ for cross-platform performance-critical code

References

Full documentation with code examples in references/:

JavaScript/React (js-*)
FileImpactDescription
js-lists-flatlist-flashlist.mdCRITICALReplace ScrollView with virtualized lists
js-profile-react.mdMEDIUMagent-device react-devtools profiling
js-measure-fps.mdHIGHFPS monitoring and measurement
js-memory-leaks.mdMEDIUMJS memory leak hunting
js-atomic-state.mdHIGHJotai/Zustand patterns
js-concurrent-react.mdHIGHuseDeferredValue, useTransition
js-react-compiler.mdHIGHAutomatic memoization
js-animations-reanimated.mdMEDIUMReanimated worklets
js-bottomsheet.mdHIGHBottom sheet optimization
js-uncontrolled-components.mdHIGHTextInput optimization
Native (native-*)
FileImpactDescription
native-turbo-modules.mdHIGHBuilding fast native modules
native-sdks-over-polyfills.mdHIGHNative vs JS libraries
native-measure-tti.mdHIGHTTI measurement setup
native-threading-model.mdHIGHTurbo Module threads
native-profiling.mdMEDIUMXcode/Android Studio profiling
native-platform-setup.mdMEDIUMiOS/Android tooling guide
native-view-flattening.mdMEDIUMView hierarchy debugging
native-memory-patterns.mdMEDIUMC++/Swift/Kotlin memory
native-memory-leaks.mdMEDIUMNative memory leak hunting
native-android-16kb-alignment.mdCRITICALThird-party library alignment for Google Play
Bundling (bundle-*)
FileImpactDescription
bundle-barrel-exports.mdCRITICALAvoid barrel imports
bundle-analyze-js.mdCRITICALJS bundle visualization
bundle-tree-shaking.mdHIGHDead code elimination
bundle-analyze-app.mdHIGHApp size analysis
bundle-r8-android.mdHIGHAndroid code shrinking
bundle-hermes-mmap.mdHIGHDisable bundle compression
bundle-native-assets.mdHIGHAsset catalog setup
bundle-library-size.mdMEDIUMEvaluate dependencies
bundle-code-splitting.mdMEDIUMRemote chunk loading safeguards

Problem → Skill Mapping

ProblemStart With
App feels slow/jankyjs-measure-fps.md → js-profile-react.md
Too many re-rendersjs-profile-react.md → js-react-compiler.md
Slow startup (TTI)native-measure-tti.md → bundle-analyze-js.md
Large app sizebundle-analyze-app.md → bundle-r8-android.md
Memory growingjs-memory-leaks.md or native-memory-leaks.md
Animation drops framesjs-animations-reanimated.md
Bottom sheet jank/re-rendersjs-bottomsheet.md → js-animations-reanimated.md
List scroll jankjs-lists-flatlist-flashlist.md
TextInput lagjs-uncontrolled-components.md
Native module slownative-turbo-modules.md → native-threading-model.md
Native library alignment issuenative-android-16kb-alignment.md

Attribution

Based on "The Ultimate Guide to React Native Optimization" by Callstack.

Files

references/native-memory-patterns.md

title: Native Memory Management impact: MEDIUM tags: memory, c++, swift, kotlin, arc, smart-pointers

Skill: Native Memory Management

Understand memory management patterns in C++, Swift, and Kotlin for React Native native modules.

Quick Reference

PatternLanguagesMechanism
Reference CountingSwift, Obj-CCount refs, free at zero
Smart pointersC++Ownership encoded in pointer type
Garbage CollectionKotlin/Java, JavaScriptGC scans and frees unreachable
ManualC, C++ (raw pointers)Explicit new/delete

Key rule: Prefer stack allocation or std::unique_ptr for single ownership; use std::shared_ptr only for real shared ownership and std::weak_ptr to break cycles. In Swift, use weak when the referenced object can disappear first; use unowned only when its lifetime is guaranteed to be at least as long.

When to Use

  • Writing native modules with manual memory management

  • Debugging native memory leaks

  • Interfacing C++ with Swift/Kotlin

  • Understanding reference counting vs garbage collection

C++ Smart Pointers

std::unique_ptr - Single Owner
#include <memory>

void takeOwnership(std::unique_ptr<std::string> s) {
    std::cout << *s;
    // Automatically deleted when function ends
}

int main() {
    auto str = std::make_unique<std::string>("Hello");
    
    // Can only be moved, not copied
    takeOwnership(std::move(str));
    // str is now empty
    
    return 0;
}
std::shared_ptr - Multiple Owners
void useShared(std::shared_ptr<std::string> s) {
    std::cout << *s;  // Reference count temporarily +1
}

void useReference(const std::shared_ptr<std::string>& s) {
    std::cout << *s;  // No ref count change (passed by reference)
}

int main() {
    auto str = std::make_shared<std::string>("Hello");
    
    useShared(str);      // Copies pointer, ref count +1
    useReference(str);   // No copy, ref count unchanged
    
    std::cout << *str;   // Still valid
    return 0;
}
std::weak_ptr - Non-Owning Reference
void useWeak(std::weak_ptr<std::string> weak) {
    if (auto shared = weak.lock()) {  // Check if still exists
        std::cout << *shared;
    } else {
        std::cout << "Object destroyed";
    }
}

int main() {
    auto str = std::make_shared<std::string>("Hello");
    std::weak_ptr<std::string> weak = str;  // No ref count increase
    
    useWeak(weak);  // Works
    str.reset();    // Destroys object
    useWeak(weak);  // "Object destroyed"
    
    return 0;
}

Swift ARC (Automatic Reference Counting)

class Person {
    let name: String
    init(name: String) { self.name = name }
    deinit { print("Deallocated") }
}

do {
    let person1 = Person(name: "John")  // Ref count: 1
    
    do {
        let person2 = person1  // Ref count: 2
    }  // person2 out of scope, ref count: 1
    
}  // person1 out of scope, ref count: 0, "Deallocated"
Breaking Reference Cycles with weak
// BAD: Reference cycle (memory leak)
class A {
    var b: B?
}
class B {
    var a: A?  // Strong reference creates cycle
}

// GOOD: Use weak to break cycle
class A {
    var b: B?
}
class B {
    weak var a: A?  // Weak reference, doesn't prevent deallocation
}

Kotlin/Android GC

Weak References for Caches

WeakHashMap weakens keys, not values. Store WeakReference values explicitly when the cached value itself should not be strongly retained. Do not rely on deterministic System.gc() behavior in tests.

WeakReference for Callbacks
class DataManager {
    // Weak references to listeners prevent memory leaks
    private val listeners = mutableListOf<WeakReference<DataListener>>()
    
    fun addListener(listener: DataListener) {
        listeners.add(WeakReference(listener))
    }
    
    fun notifyListeners(data: String) {
        listeners.forEach { ref ->
            ref.get()?.onDataChanged(data)
        }
    }
}

Common Memory Leak Sources

1. Forgetting to Delete (C++)
// BAD: Memory leak
int main() {
    std::string* str = new std::string("Hello");
    // Forgot to delete!
    return 0;
}

// GOOD: Use smart pointers or stack allocation
int main() {
    auto str = std::make_unique<std::string>("Hello");
    // Automatically deleted
    return 0;
}
2. Reference Cycles (Swift/C++)
// BAD: Cycle
class A { std::shared_ptr<B> b; };
class B { std::shared_ptr<A> a; };

// GOOD: Break with weak_ptr
class A { std::shared_ptr<B> b; };
class B { std::weak_ptr<A> a; };
3. Unremoved Listeners (Kotlin)
// BAD: Listener never removed
class MyClass {
    private val listener = object : Callback {
        override fun onEvent() { /* ... */ }
    }
    
    init {
        EventManager.addListener(listener)
        // Never removed!
    }
}

// GOOD: Implement cleanup
class MyClass : AutoCloseable {
    private val listener = object : Callback {
        override fun onEvent() { /* ... */ }
    }
    
    init {
        EventManager.addListener(listener)
    }
    
    override fun close() {
        EventManager.removeListener(listener)
    }
}

Swift Unmanaged (Advanced)

Use Unmanaged only for C interop that explicitly transfers ownership. Match passRetained with takeRetainedValue, and passUnretained with takeUnretainedValue.

Best Practices Summary

LanguageBest Practice
C++Prefer stack or unique_ptr; use shared_ptr only for shared ownership
SwiftUse weak for delegates and disappearing references; use unowned only with guaranteed lifetime
KotlinImplement AutoCloseable, use WeakReference
AllPrefer stack over heap when possible

Related Skills

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs Node.js

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Published by
Callstack
Publisher
Callstack (Official)
Source
callstackincubator/agent-skills · skills/react-native-best-practices · commit 59e9d17
Licence
MIT License (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
Synced

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