Skill file

Logcat — capture, filter, triage

Published Nov 9, 2026

Fetch this skill (agents and humans alike):

curl https://droidskills.dev/logcat/SKILL.md

Logcat — capture, filter, triage

Logcat is the command-line view into the device’s log buffers: system and app messages, including stack traces. The official reference is developer.android.com/tools/logcat (verified live 2026-11-09; the buffer flags -b main, -b radio, -b events and the *:S silencer were confirmed on that page, same retrieval).

Golden rule: capture before you clear. Reading logs changes nothing on the device, but adb logcat -c discards buffer contents — run it only after the evidence is saved, never before.

The five commands that cover most tasks

adb logcat -d                    # dump the current buffer and exit (no streaming)
adb logcat -d -t 200             # only the last 200 lines
adb logcat -d '*:W'              # warnings and worse, every tag
adb logcat -d MyTag:D '*:S'      # one tag at debug+, silence everything else
adb logcat -d -b crash           # the crash buffer (fatal-error stack traces)

Filter syntax is <tag>:<priority>, where priority is V(erbose), D(ebug), I(nfo), W(arn), E(rror), or F(atal). Add *:S to silence every tag you did not name — without it you widen the output instead of narrowing it. (Filter grammar verified on the official page. The -b crash buffer is self-verifying: run it — an invalid buffer name fails immediately.)

Capture one app’s output

  1. Find the process: adb shell pidof com.example.app prints the PID (the app must be running; pidof is a standard shell utility on the device).
  2. Filter by it: adb logcat -d --pid 12345.
  3. PIDs are per-process-instance — if the app restarts, repeat both steps.

Triage a crash report (the recipe)

adb logcat -d -b crash -t 100 > crash.txt, then read bottom-up for the FATAL EXCEPTION block: its first line names the exception type, and the first app frame in the stack is the prime suspect. Pair the stack with the main buffer around the same timestamps (adb logcat -d -t 500) for the lead-up.

Verify the pipeline

adb logcat -d -t 5 — five lines from the device means transport and permissions are working. Silence means the device is not connected or not authorized: see the ADB skill.