Mobile Perf Auditor

Mobile Performance Auditor Protocol

Mobile devices have hard constraints on memory, CPU, and battery. What works fine on a fast developer machine or simulator might cause a crash or severe battery drain on a 4-year-old device. This skill analyzes performance metrics to find the root cause of sluggishness or resource exhaustion.

Core principle: Blaming the user's device is not an option. Find the bottleneck in the code.

Workflow

1. Identify the performance symptom (e.g., slow start, UI stutter, OOM crashes)
2. Determine the context (iOS, Android, React Native, Platform context)
3. Request or analyze profiling data / metrics
4. Correlate metrics with common architectural anti-patterns
5. Propose a targeted, measurable fix

Step 1: Symptom Identification

Categorize the user's complaint:

• Cold Start: Time from tapping the icon to the first meaningful interaction.
• Jank/Stutter: Framerate dropping below 60fps (or 120fps) during scrolling or animations.
• Memory/OOM: Out Of Memory crashes caused by leaks or large resource allocation.
• Battery/Thermal: Phone getting hot or draining battery due to non-stop background work or GPU overwork.
• Bundle Size: App takes too long to download or exceeds over-the-air limits.

Step 2: Contextualize

Understand the environment:

• Is this native (Swift/Kotlin) or cross-platform (React Native/Flutter)?
• Is the issue happening on all devices or specific older models?

Step 3: Analyze Profiling Data

Ask for or analyze existing data from:

• iOS: Xcode Instruments (Time Profiler, Leaks, Allocations), MetricKit.
• Android: Android Studio Profiler (CPU, Memory, Network), Perfetto.
• Cross-Platform: React Native Performance Monitor, Flipper, Flutter DevTools.

Step 4: Diagnosis

Identify common culprits based on data:

• Cold start slow? Heavy synchronous work on the main thread, parsing large JSON files on mount, instantiating too many singletons.
• Scrolling jank? Re-rendering heavy lists, calculating layout inside onScroll, heavy image decoding on the UI thread.
• Memory leaks? Retain cycles (iOS/Swift closures), forgotten listeners (Android contexts), large image caches not being cleared on memory warnings.

Step 5: Actionable Mitigation

Provide a specific code-level or architecture-level fix. "Optimize your images" is not acceptable. "Use downsampling during image decode via BitmapFactory.Options.inSampleSize before loading into memory" is acceptable.

Output Format

# ⚡ Performance Audit Report

**Symptom:** [e.g., UI Scroll Jank on Android]
**Environment:** [e.g., React Native 0.72, Low-end Android devices]

## 🔍 Root Cause Analysis
Based on the provided metrics/context, the bottleneck appears to be:
[Detailed explanation of WHY this is happening. E.g., The JS thread is blocked during scroll because `setState` is being called excessively in the `onScroll` handler, causing a drop below 60FPS.]

## 🛠 Actionable Fix

### Fix 1: [Name of the fix, e.g., Debounce Scroll Events / Use Reanimated]
- **Current Pattern:** [What they are doing wrong]
- **Proposed Pattern:** [What they should do]
- **Code Example (if applicable):**
  ```javascript
  // Optimized code snippet

Fix 2: [Secondary fix or long-term architecture change]

[Explanation]

📏 Measurement Strategy

How to verify this worked: [E.g., "Run the React Native Performance Monitor. You should see the JS thread maintain 60FPS during aggressive scrolling, and the UI frame time should drop below 16ms."]

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## When to Skip
- The user is asking about network API response times (that is backend latency, not mobile client performance).
- The user is asking about web browser performance (use a web/Lighthouse skill).

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## Guardrails
- **Main Thread Rule:** Always prioritize freeing up the Main/UI thread. Never suggest solutions that move heavy work back to the main thread.
- **No Silver Bullets:** Do not blindly recommend caching or memoization without proving that re-computation is actually the bottleneck. Over-memoizing causes memory issues.

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## References
See `references/EXAMPLES.md` for a worked case.

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## 🔗 Next Steps & Handoffs
If you are executing the **Pre-Release Audit Flow** as defined in the Mobile ECOSYSTEM guide, and this performance audit passes, the next mandatory skill in the sequence is:
- `@mobile-security-auditor`

If you are executing the **Post-Launch Monitoring Flow** and have successfully optimized the app based on a crash/jank report, the flow concludes here or hands back to:
- `@crash-analyst` (to verify the fix in the next release)