Scout Flutter

Zero-config OpenTelemetry RUM (Real User Monitoring) for Flutter. One package, one initialize() call — and the SDK captures spans, metrics, and logs for taps, navigation, errors, lifecycle, crashes, performance, and network out of the box.

• Package — https://pub.dev/packages/scout_flutter
• Integration guide — doc/scout-flutter-guide.md
• Publisher — base14.io

What's Captured

Auto-captured (zero code changes)

Signal	Span/Metric	Details
Taps	user_interaction	Buttons, GestureDetectors, InkWells, Switches, Tabs
Lifecycle	app_paused, app_resumed	Background/foreground transitions
Errors	error.count metric	FlutterError + uncaught async exceptions
Device info	Resource attributes	Model, manufacturer, battery level, connectivity
App startup	app_startup	Cold start and warm start duration
Long tasks	long_task	Main isolate jank detection (configurable threshold)
ANR	anr	Native watchdog thread detects unresponsive main thread
Frame metrics	flutter.frame.build_time, flutter.frame.raster_time	Per-frame build and raster histograms
Frozen frames	frozen_frame	Frames exceeding 700ms
Memory	flutter.memory.usage	Periodic native memory gauge
CPU	flutter.cpu.usage	Periodic CPU usage percentage gauge
Crash detection	app_crash	Detects OOM/SIGKILL/exit crashes via session marker
Native crashes	native_crash	JVM exceptions, NDK signals (SIGSEGV, SIGABRT, etc.) with full stack trace, registers, memory map

With navigator observer

Signal	Span	Details
Screen views	screen_view	Auto-named from route settings or widget type
Screen load time	screen_load	Time from push to first frame rendered
View sessions	view_session	Time spent on each screen

With network tracking (enabled by default)

Signal	Span	Details
HTTP requests	http.request	Method, URL, status, duration, response size
Distributed tracing	W3C traceparent	Injected for first-party hosts

Structured logging

Signal	Export	Details
Logs	OTLP logs	Debug, info, warning, error severity levels
Print capture	OTLP logs	Optional debugPrint() capture as info-level logs

Crash Detection

Three categories of crashes:

• Session marker (app_crash) — OOM kills, exit() calls, and SIGKILL via persistent marker file. Reported on the next launch with the crashed session's breadcrumbs.
• JVM / NSException (native_crash) — uncaught Java/Kotlin exceptions on Android, NSExceptions on iOS. Written to disk before the process dies.
• Native signals (native_crash) — SIGSEGV, SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGTRAP on Android via a C signal handler. Captures stack trace via frame-pointer walk, register dump, signal code, pid/tid/uid, memory map, ABI, build fingerprint, kernel version, process uptime.

Breadcrumbs are persisted to disk on every record, so they survive crashes and ship with both app_crash and native_crash spans.

SDK Crash Safety

Every telemetry callback, error handler, and export path is wrapped in try/catch. If any telemetry operation fails, it silently degrades — your app continues running normally.

Sampling

By default Scout samples 1% of sessions (sessionSampleRate: 1.0). When a session is sampled, every span in it is recorded; otherwise the whole session is dropped, so session traces stay coherent.

Error- and crash-class spans (error, native_crash, app_crash, anr, ui_hang) bypass the session sample rate by default. Set alwaysCaptureErrors: false to subject them to the same gate. Sampling is enforced at the OpenTelemetry layer, so it also applies to spans emitted by auto-instrumentation and direct tracer.startSpan calls.

Debug Logging

Set debugLogging: true to print a [scout] line for every init, session rotation, sampling decision, export batch, and log entry. Useful while integrating; noisy in production.

[scout] init ok (service=my-app endpoint=http://localhost:4318 v=1.0.0 sampleRate=1.0 alwaysCaptureErrors=true)
[scout] session a1b2c3 sampled=true
[scout] span screen_view → recordAndSample
[scout] span http.request → drop
[scout] export batch: 8 spans (212ms) ok
[scout] log [warn] Retry attempt 2

Public API surface

• ScoutFlutter.initialize(config: ...) — boot the SDK
• ScoutFlutter.navigatorObserver — navigation/screen tracking
• ScoutFlutter.dioInterceptor — Dio HTTP interceptor (apps using dart:io HttpClient are tracked automatically)
• ScoutFlutter.observeScroll(child: ...) — scroll-depth instrumentation
• ScoutFlutter.logEvent(name, attributes: ...) — custom business events
• ScoutFlutter.logInfo/logWarning/logError/logDebug(...) — structured logging
• ScoutFlutter.addBreadcrumb(type, message) — error context
• ScoutFlutter.reportError(error, stackTrace) — manual error reporting
• ScoutFlutter.setUser(id: ..., attributes: ...) / clearUser() — user identity
• RumUserActionAnnotation — custom tap labels for non-standard widgets
• beforeSend config — filter or modify events before export

See the integration guide for full configuration reference and usage examples.

Architecture

Telemetry is exported via OpenTelemetry Protocol (OTLP) over HTTP:

• Traces — spans for user interactions, navigation, crashes, HTTP requests
• Metrics — histograms and gauges for frame times, memory, CPU
• Logs — structured log records with severity levels

Data flows through a beforeSend filter, then to the OTLP collector. Failed exports are queued offline and retried when connectivity returns.

Platform Support

Platform	Taps	Lifecycle	Errors	Navigation	Crashes	ANR	Native Vitals
Android	Yes	Yes	Yes	Yes	Yes	Yes	Yes
iOS	Yes	Yes	Yes	Yes	Partial	Yes	Yes

iOS crash detection covers session marker crashes and NSExceptions. Native signal handling (SIGSEGV etc.) is Android-only currently.

License

MIT