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

bash

# 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)

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

Method 2: devicectl (CLI - Recommended)

bash

# 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

bash

# 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

•Window > Devices and Simulators
•Select device
•Click "Open Console"
•Or: View device logs for crash reports

iOS Log Predicate Examples

bash

# 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

Level	Description
`default`	Default messages
`info`	Informational
`debug`	Debug (hidden by default)
`error`	Error conditions
`fault`	Fault/critical

Android Logs

Method 1: adb logcat (CLI)

bash

# 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)

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

Method 3: pidcat (Better CLI Tool)

bash

# 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

Letter	Priority
V	Verbose
D	Debug
I	Info
W	Warn
E	Error
F	Fatal
S	Silent

adb logcat Format Options

bash

# 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

bash

# 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

bash

# 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

bash

# 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:

typescript

// 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

bash

# 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

bash

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

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

Monitor Memory

bash

# 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:

bash

# 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

bash

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

Android: Ensure log level is set correctly

kotlin

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

Best Practices

•Use structured logging - Include context in log messages
•Add timestamps - Helps correlate events
•Filter early - Don't stream all logs
•Save important logs - Redirect to file for later analysis
•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