iOS and Android Device Logs

iOS and Android Device Logs

Complete guide to viewing and filtering device logs on iOS and Android.

When to Use This Skill

• User needs to see device logs
• User is debugging crashes
• User wants to filter logs by app
• User needs real-time log streaming
• User asks "how to see logs"

Quick Commands

# iOS - Stream logs from connected device
xcrun devicectl device log stream --device <UUID>

# iOS - Stream from simulator
xcrun simctl spawn booted log stream

# Android - Stream all logs
adb logcat

# Android - Filter by package
adb logcat --pid=$(adb shell pidof com.yourapp.id)

iOS Logs

Method 1: Console.app (GUI)

1. Open Console.app (Applications > Utilities)
2. Select your device in sidebar
3. Click "Start Streaming"
4. Use search to filter:
   • By process: process:YourApp
   • By subsystem: subsystem:com.yourapp
   • By message: "error"

Method 2: devicectl (CLI - Recommended)

# List connected devices
xcrun devicectl list devices

# Stream logs from specific device
xcrun devicectl device log stream --device <DEVICE_UUID>

# Stream with predicate filter
xcrun devicectl device log stream --device <DEVICE_UUID> \
  --predicate 'process == "YourApp"'

# Stream specific log levels
xcrun devicectl device log stream --device <DEVICE_UUID> \
  --level error

# Save to file
xcrun devicectl device log stream --device <DEVICE_UUID> \
  --predicate 'process == "YourApp"' > app_logs.txt

Method 3: simctl for Simulators

# Stream logs from booted simulator
xcrun simctl spawn booted log stream

# Filter by process
xcrun simctl spawn booted log stream --predicate 'process == "YourApp"'

# Filter by subsystem
xcrun simctl spawn booted log stream --predicate 'subsystem == "com.yourapp"'

# Show only errors
xcrun simctl spawn booted log stream --level error

# Combine filters
xcrun simctl spawn booted log stream \
  --predicate 'process == "YourApp" AND messageType == error'

Method 4: Xcode Device Logs

1. Window > Devices and Simulators
2. Select device
3. Click "Open Console"
4. Or: View device logs for crash reports

iOS Log Predicate Examples

# Process name
--predicate 'process == "YourApp"'

# Contains text
--predicate 'eventMessage contains "error"'

# Subsystem
--predicate 'subsystem == "com.yourapp.plugin"'

# Category
--predicate 'category == "network"'

# Log level
--predicate 'messageType == error'

# Combined
--predicate 'process == "YourApp" AND messageType >= error'

# Time-based (last 5 minutes)
--predicate 'timestamp > now - 5m'

iOS Log Levels

Android Logs

Method 1: adb logcat (CLI)

# Basic log stream
adb logcat

# Clear logs first, then stream
adb logcat -c && adb logcat

# Filter by tag
adb logcat -s MyTag:D

# Filter by priority
adb logcat *:E  # Only errors and above

# Filter by package name
adb logcat --pid=$(adb shell pidof com.yourapp.id)

# Filter by multiple tags
adb logcat -s "MyPlugin:D" "Capacitor:I"

# Save to file
adb logcat > logs.txt

# Save to file with timestamp
adb logcat -v time > logs.txt

Method 2: Android Studio Logcat (GUI)

1. View > Tool Windows > Logcat
2. Use filter dropdown:
   • Package: package:com.yourapp
   • Tag: tag:MyPlugin
   • Level: level:error
3. Create saved filters for quick access

Method 3: pidcat (Better CLI Tool)

# Install pidcat
pip install pidcat

# Stream logs for package
pidcat com.yourapp.id

# With tag filter
pidcat -t MyPlugin com.yourapp.id

Android Log Priority Levels

adb logcat Format Options

# Different output formats
adb logcat -v brief     # Default
adb logcat -v process   # PID only
adb logcat -v tag       # Tag only
adb logcat -v time      # With timestamp
adb logcat -v threadtime # With thread and time
adb logcat -v long      # All metadata

# Colorized output
adb logcat -v color

# Show recent logs (last N lines)
adb logcat -d -t 100

# Show logs since timestamp
adb logcat -v time -T "01-25 10:00:00.000"

Common Android Filters

# Capacitor core logs
adb logcat -s "Capacitor:*"

# Plugin-specific logs
adb logcat -s "CapacitorNativeBiometric:*"

# WebView logs (JavaScript console)
adb logcat -s "chromium:*"

# JavaScript errors
adb logcat | grep -i "js error\|uncaught"

# Crash logs
adb logcat | grep -iE "fatal|crash|exception"

# Network logs
adb logcat -s "OkHttp:*" "NetworkSecurityConfig:*"

Viewing Crash Logs

iOS Crash Logs

# Copy crash logs from device
xcrun devicectl device copy crashlog --device <UUID> ./​crashes/

# View in Console.app
# User Diagnostics Reports section

# Or find at:
# Device: Settings > Privacy > Analytics & Improvements > Analytics Data
# Mac: ~/​Library/​Logs/​DiagnosticReports/

Android Crash Logs

# Get tombstone (native crash)
adb shell cat /​data/​tombstones/​tombstone_00

# Get ANR traces
adb pull /​data/​anr/​traces.txt

# Get bugreport (comprehensive)
adb bugreport > bugreport.zip

MCP Integration

Use MCP tools to fetch logs programmatically:

// Example MCP tool for fetching iOS logs
const logs = await mcp.ios.streamLogs({
  device: 'booted',
  predicate: 'process == "YourApp"',
  level: 'debug',
});

// Example MCP tool for Android logs
const androidLogs = await mcp.android.logcat({
  package: 'com.yourapp.id',
  level: 'D',
});

Log Parsing Tips

Extract JavaScript Errors

# iOS - JavaScript console logs
xcrun simctl spawn booted log stream \
  --predicate 'eventMessage contains "JS:"'

# Android - WebView console
adb logcat chromium:I *:S | grep "console"

Filter Network Requests

# iOS
xcrun simctl spawn booted log stream \
  --predicate 'subsystem == "com.apple.network"'

# Android
adb logcat -s "NetworkSecurityConfig:*" "OkHttp:*"

Monitor Memory

# iOS - Memory pressure
xcrun simctl spawn booted log stream \
  --predicate 'eventMessage contains "memory"'

# Android - Memory info
adb shell dumpsys meminfo com.yourapp.id

Troubleshooting

Issue: No Logs Showing

iOS:

• Ensure device is trusted: Xcode > Window > Devices
• Try restarting log stream
• Check Console.app filters

Android:

• Enable USB debugging
• Run adb devices to verify connection
• Try adb kill-server && adb start-server

Issue: Too Many Logs

Use filters:

# iOS - Only your app
--predicate 'process == "YourApp" AND messageType >= info'

# Android - Only your package
adb logcat --pid=$(adb shell pidof com.yourapp.id)

Issue: Missing Debug Logs

iOS: Debug logs are hidden by default

# Enable debug logs
xcrun simctl spawn booted log stream --level debug

Android: Ensure log level is set correctly

Log.d("Tag", "Debug message")  // D level

Best Practices

1. Use structured logging - Include context in log messages
2. Add timestamps - Helps correlate events
3. Filter early - Don't stream all logs
4. Save important logs - Redirect to file for later analysis
5. Use log levels appropriately - Debug for dev, error for production

Resources

• iOS Unified Logging: https://developer.apple.com/documentation/os/logging
• Android Logcat: https://developer.android.com/studio/debug/logcat
• devicectl Reference: https://developer.apple.com/documentation/devicemanagement