log_stream

The log_stream tool captures live, real-time log output from a booted simulator or connected physical device. It uses Apple’s unified logging system (os_log) under the hood, allowing you to apply powerful predicate filters to isolate logs from specific subsystems, categories, or processes. The stream runs for a configurable duration and returns the captured entries.

Parameters

Parameter	Type	Required	Default	Description
`deviceId`	string	Yes	—	UDID of the simulator or physical device to stream logs from.
`predicate`	string	No	—	NSPredicate-style filter expression (e.g., `subsystem == "com.example.app"`).
`level`	enum	No	`"default"`	Minimum log level to include. One of `"default"`, `"info"`, or `"debug"`.
`timeout`	number	No	`10`	Duration in seconds to capture the log stream before automatically stopping.

Usage Examples

Stream all logs from a simulator for 10 seconds

“Show me live logs from my iPhone 16 Pro simulator”

{
  "deviceId": "A1B2C3D4-E5F6-7890-ABCD-EF1234567890"
}

Filter logs to a specific app subsystem

“Stream logs from my WeatherApp on the booted simulator”

{
  "deviceId": "A1B2C3D4-E5F6-7890-ABCD-EF1234567890",
  "predicate": "subsystem == \"com.myteam.WeatherApp\"",
  "level": "debug",
  "timeout": 15
}

Monitor networking activity

“Stream only network-related logs from my app for 20 seconds”

{
  "deviceId": "A1B2C3D4-E5F6-7890-ABCD-EF1234567890",
  "predicate": "subsystem == \"com.myteam.WeatherApp\" AND category == \"networking\"",
  "level": "info",
  "timeout": 20
}

Capture error-level logs across the entire system

“Show me all default-level-and-above logs from the simulator for 5 seconds”

{
  "deviceId": "A1B2C3D4-E5F6-7890-ABCD-EF1234567890",
  "level": "default",
  "timeout": 5
}

Example Output

2026-02-23 14:32:01.234  WeatherApp[1842:67890] [networking] Starting request: GET https://api.weather.example.com/v1/forecast?lat=37.7749&lon=-122.4194
2026-02-23 14:32:01.567  WeatherApp[1842:67890] [networking] Response received: 200 OK (245 bytes, 333ms)
2026-02-23 14:32:01.589  WeatherApp[1842:67891] [viewmodel] Decoded 7-day forecast for San Francisco
2026-02-23 14:32:01.602  WeatherApp[1842:67891] [ui] Refreshing ForecastListView with 7 items
2026-02-23 14:32:02.105  WeatherApp[1842:67892] [coredata] Saved forecast snapshot to persistent store
2026-02-23 14:32:05.001  WeatherApp[1842:67890] [networking] Starting request: GET https://api.weather.example.com/v1/alerts?lat=37.7749&lon=-122.4194
2026-02-23 14:32:05.210  WeatherApp[1842:67890] [networking] Response received: 200 OK (82 bytes, 209ms)
2026-02-23 14:32:05.230  WeatherApp[1842:67891] [viewmodel] No active weather alerts for region

Stream ended after 15 seconds. 8 log entries captured.

log_collect — Collect historical logs from a past time range instead of streaming live.
app_launch — Launch an app with console output captured at startup.
diagnostics — Collect a full diagnostic report including system logs, crash reports, and more.