iOS Instruments Performance CLI

Instructions

When helping with iOS app performance optimization using Instruments command line tools:

1. Setup Analysis Environment

CRITICAL: Always use device UUID, never device names

Get device UUID: xcrun simctl list devices available | grep "iPhone"
Device names like "iPhone 17 Pro" are ambiguous and will fail
Use UUID format: F464E766-555C-4B95-B8CC-763702A70791

Clean installation state (REQUIRED)

Always uninstall app before profiling: xcrun simctl uninstall $DEVICE_UUID <bundle id>
Multiple app installations cause "process is ambiguous" errors
Alternative: Completely erase simulator for cleanest state

Build configuration

Build in Release mode for accurate performance measurements

2. Choose Appropriate Instrument Template

Use xcrun xctrace list templates to see available templates:

App Launch - Essential for launch time optimization (most common)
Time Profiler - CPU performance analysis
Allocations - Memory usage tracking
Leaks - Memory leak detection
Network - API calls and network activity
Animation Hitches - UI performance issues

3. Run Performance Analysis

Standard workflow:

DEVICE_UUID="F464E766-555C-4B95-B8CC-763702A70791" # this is sample uuid, run command line to get exist uuid
xcrun simctl uninstall $DEVICE_UUID <bundle id>
xcrun simctl install $DEVICE_UUID /path/to/<app name>.app
sleep 2
xcrun xctrace record --template "App Launch" --device $DEVICE_UUID \
  --launch -- /path/to/<app name>.app 2>&1

Important notes:

Trace files auto-generate names like Launch_<app name>.app_2025-10-30_3.55.40 PM_39E6A410.trace
--output parameter may be ignored; accept auto-generated names
Wait 2 seconds after installation before profiling
Use 2>&1 to capture all output
Recording duration: 10-30s for launch, 2-5m for other analyses

4. Analyze Results

Finding trace files:

ls -lt *.trace | head -1  # Most recent trace
find . -name "*.trace" -type d -mmin -5  # Files from last 5 minutes

Analysis approaches:

CLI export often fails - "trace is malformed" errors are common
Recommended: Open in Instruments.app GUI for reliable analysis
```
open -a Instruments.app Launch_<app name>*.trace
```
Parse signpost markers for performance metrics
Identify bottlenecks in launch sequence, memory allocations, CPU hotspots

5. Common Optimization Patterns

Based on successful optimizations:

Lazy initialization - Defer expensive dependency resolution
Background operations - Move non-critical setup off main thread
Deferred bindings - Set up subscriptions after UI appears
Font loading - Register fonts asynchronously
Method swizzling - Only essential swizzles during launch

Critical Pitfalls to Avoid

❌ Using device names instead of UUIDs ❌ Skipping clean installation step ❌ Building in Debug mode ❌ Trying to export trace immediately after recording ❌ Assuming --output path will be used ❌ Not waiting between installation and profiling

Reference Documentation

See examples in this skill directory for:

Detailed command examples with correct syntax
Complete troubleshooting guide with solutions
Real-world lessons learned
Production-ready workflow scripts

ios-instruments-performance-cli