android-runtime-flag-probe

Android Runtime Flag Probe — Framework Debug Without Code Changes

When to use

• "Is the view bigger than I think?" — debug.layout true overlays bounds
• "Is overdraw killing scroll perf?" — debug.hwui.show_layers_updates true
• "Are frames missing the budget?" — debug.hwui.profile true
• "Is this animation hiding a logic bug?" — window_animation_scale 5 slows everything
• "Is Choreographer complaining about slow frames?" — log.tag.Choreographer VERBOSE
• "Is ActivityManager firing the lifecycle transition I expect?" — log.tag.ActivityManager VERBOSE

When NOT to use

• The diagnostic needs your code's data — use android-probe-logging
• The diagnostic needs precise timing — use android-trace-sections
• The diagnostic should ship — that's a permanent change behind BuildConfig.DEBUG, not an ephemeral probe

Pre-flight: detect what your device allows

# 1. adb device authorized
adb devices                              # expect "<id>  device"

# 2. Build type — userdebug/eng images honor every flag; user (production)
#    images silently no-op some setprops
adb shell getprop ro.build.type          # expect "userdebug" or "eng"

# 3. Some debug.* properties require root or system_app context — check before
#    trusting that a flip took
adb shell getprop ro.debuggable          # 1 = full debug; 0 = production-locked

On user (production) builds, the following often silently no-op (the setprop returns success but the system ignores the value):

• debug.cpu.throttle (any value)
• debug.hwui.show_layers_updates (some OEM skins)
• debug.atrace.tags.enableflags

The settings put global window_animation_scale family always works because it lives in the Settings provider, not in system properties. debug.layout and log.tag.<Tag> work everywhere.

getprop returning empty after setprop is a common gotcha — it usually means the property exists but no consumer is reading it on this device. The flag isn't broken on your end; the OS image just doesn't honor it. Try the equivalent flag from the Settings provider, or use android-trace-sections for the same diagnostic.

No root, no userdebug. That's the common case. Stick to debug.layout, log.tag.<Tag>, debug.hwui.profile, and the settings put global ..._animation_scale family — those work on every device.

The flag catalog

Logging verbosity (per tag)

adb shell setprop log.tag.<Tag> VERBOSE

The framework reads this at Log.isLoggable(tag, level) time, so it works without app restart for tags checked dynamically. For tags checked once at startup, force-stop and re-launch the app.

Tag	Surfaces
Choreographer	Frame skips, "Skipped N frames" warnings escalate to verbose
ViewRootImpl	Touch dispatch, layout passes, draw scheduling
ActivityManager	Activity lifecycle transitions, ANR details
ConnectivityService	Network state changes
WindowManager	Window add/remove, focus changes
InputDispatcher	Touch dispatch internals

HTTP libraries don't honor log.tag.<Tag>. OkHttp, Ktor, Retrofit, etc. don't read Android's Log.isLoggable — they use their own logger interfaces (e.g. HttpLoggingInterceptor for OkHttp). To get HTTP logging you have to wire the library's interceptor in code, which makes it a android-probe-logging task, not a runtime-flag one.

Layout / rendering diagnostics

adb shell setprop debug.layout true

Overlays a yellow border around every view's bounds. Excellent for "padding looks wrong but I'm not sure what's actually rendering."

adb shell setprop debug.hwui.show_layers_updates true

Flashes the screen green where layers update — useful for finding overdraw or unnecessary invalidations.

adb shell setprop debug.hwui.profile true

Renders frame-time bars at the bottom of the screen (the "GPU profiling" toggle from Developer Options). The colored stacks correspond to frame phases; bars over the green line are dropped frames.

adb shell setprop debug.hwui.overdraw show

Tints surfaces by overdraw count (blue = 1×, green = 2×, red = 4×+). Pairs well with scroll-jank investigations.

System Settings (longer-lived)

These use settings put rather than setprop:

adb shell settings put global window_animation_scale 5
adb shell settings put global transition_animation_scale 5
adb shell settings put global animator_duration_scale 5

5× animation slowdown surfaces logic bugs that flash by at normal speed. Reset to 1 when done.

adb shell settings put global ANGLE_GLES_DRIVER_ALL_ANGLE 1

(Forces the ANGLE GL driver — niche, for graphics regressions.)

Workflow

1. Pick the smallest set of flags that answers the question

Don't flip everything. One or two flags per investigation. If you flip ten flags, you can't attribute observations to any one of them.

2. Apply the flags

# Track what you flipped — write a reset script first
cat > /tmp/runtime-flag-reset.sh <<'EOF'
#!/usr/bin/env bash
adb shell setprop log.tag.Choreographer ""
adb shell setprop debug.layout false
adb shell settings put global window_animation_scale 1
EOF
chmod +x /tmp/runtime-flag-reset.sh

# Then apply
adb shell setprop log.tag.Choreographer VERBOSE
adb shell setprop debug.layout true
adb shell settings put global window_animation_scale 5

Always write the reset script first. That's the cleanup gate's input — and it ensures you can't forget what you toggled.

3. Restart the app for flags read at startup

Some flags only take effect on cold start:

adb shell am force-stop com.example.app
android run                              # or your usual deploy

debug.layout is live; log.tag.<Tag> is live for Log.isLoggable checks but cached for tags evaluated at class load.

4. Drive the suspect flow + observe

For visual flags (debug.layout, hwui.profile, hwui.overdraw), capture a screenshot:

android screen capture -o /tmp/runtime-flag-screen.png

For log-tag flags, dump filtered logcat:

adb logcat -d -s Choreographer:V ActivityManager:V > /tmp/runtime-flag-log.txt

Delegate parsing to a Sonnet sub-agent if either output is non-trivial.

5. Cleanup gate (BLOCKING — most-skipped step in the suite)

bash /tmp/runtime-flag-reset.sh

Then verify each flag is actually back to default:

adb shell getprop debug.layout                # expect empty or false
adb shell getprop log.tag.Choreographer       # expect empty
adb shell settings get global window_animation_scale   # expect 1

The classic failure mode of this skill: leaving debug.layout true on the emulator. Every screenshot in the next investigation has yellow borders, the agent thinks the UI is broken, and chases ghosts. Always verify the reset, don't just run the script.

rm -f /tmp/runtime-flag-reset.sh /tmp/runtime-flag-screen.png /tmp/runtime-flag-log.txt

Reset reference (copy-paste)

If you've forgotten what you toggled, this resets the common flags:

adb shell setprop debug.layout ""
adb shell setprop debug.hwui.show_layers_updates ""
adb shell setprop debug.hwui.profile ""
adb shell setprop debug.hwui.overdraw ""
adb shell settings put global window_animation_scale 1
adb shell settings put global transition_animation_scale 1
adb shell settings put global animator_duration_scale 1

# Reset all log.tag overrides — there's no batch reset, so list yours
for tag in Choreographer ViewRootImpl ActivityManager ConnectivityService WindowManager InputDispatcher; do
    adb shell setprop log.tag.$tag ""
done

Common mistakes

Mistake	Fix
Skipping the cleanup gate	Verify each flag is reset with getprop / settings get — the reset script is necessary but not sufficient
Flipping ten flags at once	One or two flags per investigation; otherwise observations aren't attributable
Forgetting to write the reset script first	Toggle and reset in one breath; otherwise you'll forget what you flipped
Forgetting force-stop after a tag flip	Some tags are cached at class load; restart the app to pick up the new level
Leaving window_animation_scale 5 on	Every later investigation runs in slow-motion — devastating to productivity
Trusting the reset script ran cleanly	A typo in the path silently no-ops; always verify with getprop
Flipping debug.layout and not capturing a screenshot	The overlay is visual — you need a screenshot to read it
Using setprop for window_animation_scale (it's a settings)	Animation scales live in settings global, not system properties