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Flutter

scout_flutter is a single Dart package that ships zero-config OpenTelemetry RUM for Flutter on iOS, Android, macOS, and web. Auto- captures the full Real User Monitoring event set (except Session Replay and Profiling) and exports it as OTLP traces, metrics, and logs to a Scout collector.

await ScoutFlutter.initialize(
  config: ScoutFlutterConfig(
    serviceName: 'my-app',
    endpoint: 'https://otel.example.com',
  ),
);
runApp(const MyApp());

That's all the code you write. Every tap, navigation, HTTP request, error, crash, scroll, and frame metric is gathered automatically — no manual Scout.track(...) calls anywhere in your app.

What You Get​

CapabilitySignalMechanism
Tap trackinguser_interaction span (type=tap, target, name_source, permanent_id, x/y)Global GestureBinding.instance.pointerRouter interception
Screen / route navigationscreen_view span with view.id, view.loading_type, view.referrer, view.is_activeAutoNameNavigatorObserver attached to every Navigator
Screen load timescreen_load span with screen.load_timeFirst-frame measurement after route push
App startupapp_startup span with app_startup.type = cold | warm, app_startup.durationWidgetsBinding.addPostFrameCallback on first frame
FBC vital (First Build Complete)app_vital span with vital.name = fbcEmitted alongside cold-start; ready for dashboards as a first-class vital
INV vital (Interaction → Next View)app_vital span with vital.name = inv, vital.from_screen, vital.to_screenTap timestamp correlated with next screen_view within 5 s
Errors (Flutter framework)error span with error.id, error.fingerprint, error.handled, breadcrumbsFlutterError.onError + PlatformDispatcher.instance.onError
Manual error reportingerror spanScoutFlutter.reportError(e, stackTrace)
Native crashes (iOS)native_crash span with crash.reason, registers (FAR/ESR), mach_exception, callstack_tree, binary_imagesKSCrash 2.x all five monitors + MetricKit MXCrashDiagnostic / MXHangDiagnostic
Native crashes (Android)native_crash span with crash.reason, signal info, tombstone (≤ 32 KB), crash.os_reason_*, PSS/RSSCustom NDK signal handler + ApplicationExitInfo (API 30+; reflective subReason on API 31+)
ANRanr span with anr.duration, anr.threshold, anr.thread_count, anr.threads_json, anr.main_thread_stack, and breadcrumbsiOS: AppHangWatchdog (5 s default). Android: Choreographer + ApplicationExitInfo REASON_ANR. Captures a full thread dump at detection time.
UI hang (iOS)ui_hang span with ui_hang.duration, ui_hang.thresholdiOS-only sub-ANR watchdog at 250 ms (configurable). Complements KSCrash mainThreadDeadlock and the 5 s ANR detector
Long taskslong_task span with long_task.duration, long_task.thresholdDart isolate event-loop polling
HTTP requestshttp.request span with method, URL, status, duration, headersHttpOverrides global wrap + Dio interceptor (optional)
Distributed tracingW3C traceparent header injected into outgoing requests to hosts in firstPartyHostsWrap on the HTTP client
Scroll depthdisplay.scroll.max_depth, display.scroll.max_depth_scroll_top, display.scroll.max_scroll_height, display.scroll.max_scroll_height_time_ms on screen_viewScoutScrollObserver widget wrapping NotificationListener<ScrollNotification>
Lifecycleapp_paused, app_resumed spans + force-flush on backgroundAppLifecycleListener
Frame metricsflutter.frame.build_time, flutter.frame.raster_time histogramsWidgetsBinding.instance.addTimingsCallback
Memory + CPUflutter.memory.usage, flutter.cpu.usage gaugesPlatform channel poll
Network connectivitynetwork.connection.type resource attribute (wifi, cellular, none)connectivity_plus listener
Batterydevice.battery.level, device.battery.state, device.battery.discharge_rate resource attributesbattery_plus + platform channel
Device orientationdevice.orientation resource attribute (portrait / landscape)Orientation-change listener
Device integritydevice.is_jail_broken resource attributeJailbreak / root heuristic via platform channel
LogsOTLP logsScoutFlutter.log*() and (opt-in) print / debugPrint capture
Anonymous user iduser.anonymous_id on every spanUUID v4 minted on first launch, persisted to temp dir
WebView bridgeEmbedded web pages adopt the native session.id + user.anonymous_id; their spans flow back as span.source = "webview"ScoutWebViewBridge.attach() + injectShim() on every page finish

Prerequisites​

RequirementVersion
Flutter SDK≥ 3.7.0
Dart SDK≥ 3.7.0
iOS deployment target≥ 12.0
Android minSdkVersion≥ 21 (ApplicationExitInfo features activate from API 30+)
compileSdkVersion≥ 34 (recommended)
CocoaPods≥ 1.11
NDK (Android, for native crash)≥ 25 (matches Flutter default)

Installation​

scout_flutter is published on pub.dev. Add it to your pubspec.yaml:

# pubspec.yaml
dependencies:
  scout_flutter: ^0.1.20

Or:

flutter pub add scout_flutter

iOS — CocoaPods install​

The first build after adding scout_flutter triggers a pod install for the KSCrash 2.x and MetricKit dependencies. Make sure your iOS Podfile has platform :ios, '12.0' or higher:

# ios/Podfile
platform :ios, '12.0'

Then:

cd ios && pod install --repo-update && cd ..

Android — NDK setup​

The native signal handler is built automatically as part of the plugin's Gradle build. No app-side configuration needed beyond ensuring your project has the NDK available (flutter doctor will warn if not).

Initialization​

In your main.dart, before runApp():

import 'package:flutter/material.dart';
import 'package:scout_flutter/scout_flutter.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  // Fire-and-forget — never block app startup on SDK init.
  unawaited(
    ScoutFlutter.initialize(
      config: ScoutFlutterConfig(
        serviceName: 'my-app',
        serviceVersion: '1.0.0',
        endpoint: 'https://otel.example.com',
        headers: {'Authorization': 'Bearer …'},
      ),
    ),
  );

  // Wrap your root widget with the scroll observer so per-screen
  // scroll metrics decorate the active screen_view span.
  runApp(ScoutFlutter.observeScroll(child: const MyApp()));
}

Attach ScoutFlutter.navigatorObserver to every Navigator in your app — the root MaterialApp / CupertinoApp plus each nested Navigator (commonly inside CupertinoTabView, Navigator widgets used for bottom-sheet stacks, etc.):

MaterialApp(
  navigatorObservers: [ScoutFlutter.navigatorObserver],
  // …
);

// And per CupertinoTabView:
CupertinoTabView(
  navigatorObservers: [ScoutFlutter.navigatorObserver],
  builder: (context) => const SongsTab(),
);

navigatorObserver returns a fresh instance on every read, so attaching it to multiple Navigators does not trip Flutter's "observer already has a navigator" assertion. All instances funnel events into shared static state so dashboards see one coherent screen timeline regardless of which Navigator pushed a route.

Setting user identity​

ScoutFlutter.setUser(
  id: 'user-123',
  attributes: {
    'email': 'jane@example.com',   // → user.email
    'plan': 'pro',                 // → user.plan
    'role': 'admin',               // → user.role
  },
);

// On logout:
ScoutFlutter.clearUser();

id is optional. user.id and every attribute ride on every span until cleared — bare attribute keys are auto-prefixed with user., and keys already starting with user. pass through unchanged. setUser replaces the whole user map, so pass everything you want each call.

Setting session attributes​

Session attributes attach to every subsequent span, metric, and log for the rest of the session. Keys are stored verbatim (no auto-prefix).

// Replaces all existing session attributes.
ScoutFlutter.setSessionAttributes({'tenant': 'acme', 'ab_bucket': 'B'});

// Add one without clobbering the rest — merge with the current view:
ScoutFlutter.setSessionAttributes({
  ...ScoutFlutter.sessionAttributes,
  'feature.new_checkout': 'true',
});

// Clear all.
ScoutFlutter.clearSessionAttributes();

They persist until you call clearSessionAttributes() — they are not cleared automatically on session rotation.

Configuration​

ScoutFlutterConfig is the single config object. Required fields are flagged below; everything else has a sensible default and is opt-in.

Identity​

FieldTypeDefaultDescription
serviceNameString(required)Logical app identifier. Used as service.name.
endpointString(required)OTLP-HTTP collector URL. /v1/traces, /v1/metrics, /v1/logs are appended automatically.
serviceVersionString?nullMaps to service.version. Set to your app build version.
securebooltrueWhen endpoint has no scheme, prefix https:// (true) or http:// (false).
headersMap<String, String>?nullExtra HTTP headers on every OTLP export. Use for auth.
resourceAttributesMap<String, String>?nullExtra attributes merged into every signal's Resource. Use for deployment.region, team, etc. Static — set once at init.

Network​

FieldTypeDefaultDescription
enableNetworkTrackingbooltrueWraps HttpOverrides globally. Disable if you wire ScoutFlutter.dioInterceptor manually.
firstPartyHostsList<String>?nullHosts that receive a W3C traceparent header for distributed tracing. Supports exact match or *.host wildcards.
ignoreUrlPatternsList<RegExp>?nullURLs matching any pattern are not auto-instrumented.

Sessions​

FieldTypeDefaultDescription
sessionTimeoutMinutesint30Inactivity timeout before a new session.id is minted.
maxSessionDurationMinutesint60Hard cap on session lifetime; rotates on the next ID read past this age regardless of activity. 0 disables.
sessionSampleRatedouble (0-100)1.0Percent of sessions sampled — default 1%. Below 100, full sessions are dropped (not individual events) so session traces stay coherent.
alwaysCaptureErrorsbooltrueError / crash / ANR-class spans bypass sessionSampleRate and are always exported. Set false to subject them to the same gate.

Thresholds​

FieldTypeDefaultMinDescription
longTaskThresholdMsint10020Dart isolate task duration that qualifies as a long_task span.
anrThresholdMsint50001000Main-thread block duration that fires an anr span.
iosHangThresholdMsint25050 (or 0 to disable)iOS only — sub-ANR ui_hang watchdog. Complements ANR (5 s) and KSCrash mainThreadDeadlock (5 s+). Catches micro-stutter / jank.
maxTombstoneBytesint1310724096Max bytes of Android ApplicationExitInfo tombstone (ANR / native post-mortem) captured per report.

Offline buffer​

When in-memory retry is exhausted, batches are persisted to disk and replayed on next initialize() or on app resume.

FieldTypeDefaultDescription
offlineBufferEnabledbooltrueMaster toggle. Set false for strict at-most-once delivery.
offlineMaxTraceItemsint5000FIFO cap on persisted span items. Oldest evicted first.
offlineMaxMetricItemsint2000Same, for metric data points.
offlineMaxLogItemsint5000Same, for log records.
maxOfflineStorageMbint5Coarse total-disk cap that runs alongside the per-signal offlineMax*Items caps — whichever limit is reached first wins.

Auto-instrumentation toggles​

Every auto-instrumentation can be turned off independently. All default to true except capturePrintStatements.

ToggleDefaultWhat you lose when set to false
enableAutoTapTrackingtrueAll user_interaction spans.
enableErrorTrackingtrueerror spans from FlutterError.onError and PlatformDispatcher.onError. Manual reportError() still works.
enableLifecycleTrackingtrueapp_paused / app_resumed spans and the background-flush hook. Heavy loss — recommend leaving on.
enableStartupTrackingtrueapp_startup cold/warm spans and the FBC vital.
enableConnectivityTrackingtruenetwork.connection.type resource attr updates on network transitions.
enablePerformanceMetricstrueflutter.memory.usage and flutter.cpu.usage gauges.
enableLongTaskDetectiontruelong_task spans. Tune with longTaskThresholdMs instead of disabling.
enableAnrDetectiontrueanr spans and the iOS ui_hang watchdog.
enableNetworkTrackingtruehttp.request spans + traceparent injection.
enableLoggingtrueScoutFlutter.log*() calls become no-ops.
capturePrintStatementsfalse(Off by default) When true, mirrors print / debugPrint calls to OTLP logs. Original console output is preserved.

Filtering — beforeSend​

ScoutFlutterConfig(
  // …
  beforeSend: (event) {
    // event keys: 'type' ('span'|'metric'|'log'), 'name', plus
    // per-span attributes. Return null to drop the event.
    if ((event['http.url'] as String?)?.contains('/health') == true) {
      return null;
    }
    event.remove('user.email');
    return event;
  },
)

Sees per-span attributes only. Resource attributes set on the OTel Resource (e.g. service.name, os.name, device.*) are not in the event payload.

Native crash setup​

iOS — KSCrash + MetricKit​

The plugin auto-installs KSCrash 2.5+ with all five monitors:

  • Mach exceptions
  • POSIX signals
  • C++ exceptions
  • NSException
  • Main-thread deadlock (5 s+ — complementary to the 250 ms iosHangThresholdMs watchdog)

On every launch, scout_flutter drains any persisted KSCrash reports from the previous run and emits them as native_crash spans carrying:

  • crash.reason, crash.type, crash.signal, crash.os_name, crash.os_version, crash.kernel
  • crash.registers_json — full CPU register dump including FAR and ESR
  • crash.mach_exception, crash.mach_code, crash.mach_subcode
  • crash.nsexception_name (when applicable)
  • crash.callstack_tree_json — symbolicated stack tree of every thread
  • crash.binary_images_json — loaded image list for offline symbolication
  • The prior session's last 20 breadcrumbs

In parallel, an MXMetricManagerSubscriber collects asynchronous MXCrashDiagnostic and MXHangDiagnostic payloads that Apple delivers the morning after a crash — useful for catching kernel-killed crashes that KSCrash couldn't intercept.

Triggering a crash (testing)​

scout_flutter does not ship a "simulate crash" API. To validate end-to-end capture, trigger a real fault — and never use exit(), which is a graceful shutdown that no crash reporter intercepts:

// Uncaught Dart error → `error` span (and, if fatal, `app_crash` on relaunch).
throw StateError('test crash');

For a true native signal (SIGSEGV on Android, fatalError() on iOS), add a small platform-channel method on the app side. The repo's example/ app and the flutter/samples/platform_design sample ship ready-made crash / ANR / deadlock buttons for exactly this.

Android — NDK signal handler + ApplicationExitInfo​

The plugin auto-installs a custom NDK signal handler that catches SIGSEGV / SIGABRT / SIGBUS / SIGILL / SIGFPE before they kill the process. A tombstone (up to 32 KB) plus signal info is persisted to disk and emitted on next launch as a native_crash span.

In parallel, on API 30+ (Android 11+), scout_flutter polls ActivityManager.getHistoricalProcessExitReasons and emits a native_crash span for any OS-recorded death newer than the persisted watermark. This captures:

  • crash.os_reason_code / crash.os_reason_name (crash, crash_native, anr, low_memory, excessive_resource_usage, initialization_failure, signaled)
  • crash.os_reason_subcode (API 31+ via reflection)
  • crash.exit_status, crash.importance, crash.death_timestamp_ms, crash.process_name, crash.pid, crash.pss_kb, crash.rss_kb
  • crash.tombstone — full thread dump (capped at 32 KB)

The two pipelines complement each other: NDK fires in-process at crash time, ApplicationExitInfo catches deaths that the OS killed before in-process handlers could write to disk (OOM, hard watchdog, etc.).

Background flush​

scout_flutter calls forceFlush() on every signal provider when the app transitions to AppLifecycleState.paused / inactive / hidden. This drains the BatchSpanProcessor, metric reader, and log processor before the OS suspends the process — without it, events emitted in the last few seconds (the ones leading up to a crash) would die with the in-memory batch queue.

If the in-memory exporter still doesn't deliver in time (OS kills us mid-POST), the offline buffer persists the batch to disk and replays it on next initialize().

WebView bridge​

Embed a WebView showing a page instrumented with @base14/scout-react (web entry) v0.1.5+, and scout_flutter will flatten the WebView's RUM session into the native session — both runtimes share one session.id and user.anonymous_id, and the embedded page's spans flow back into the native pipeline tagged with span.source = "webview".

import 'package:scout_flutter/scout_flutter.dart';
import 'package:webview_flutter/webview_flutter.dart';

final controller = WebViewController()
  ..setJavaScriptMode(JavaScriptMode.unrestricted)
  ..setNavigationDelegate(
    NavigationDelegate(
      onPageFinished: (_) {
        // Re-inject the shim on every navigation. The shim has a
        // sentinel so re-injecting in the same page is a no-op.
        ScoutWebViewBridge.injectShim(
          runJavaScript: controller.runJavaScript,
        );
      },
    ),
  );

ScoutWebViewBridge.attach(
  addJavaScriptChannel: (name, onMessage) {
    controller.addJavaScriptChannel(
      name,
      onMessageReceived: (m) => onMessage(m.message),
    );
  },
);

await controller.loadRequest(Uri.parse('https://app.example.com'));

The bridge:

  1. Registers a JavaScript channel (default name ScoutBridge) the page can postMessage into.
  2. Injects a JS shim that polls window.Scout and calls setWebViewBridge({sessionId, anonymousId, send}) once the page's web SDK appears.
  3. Receives bridged span payloads via the channel and re-emits them as native spans with span.source = "webview", session.id, user.anonymous_id, and the rest of the native common attributes.

The bridge is currently a parallel transport — both the web SDK's own OTLP exporter and the native bridge ship a copy of each span. Configure the web SDK with an unreachable endpoint, or filter everything with beforeSend returning null, to make the bridge the sole transport.

The bridge is generic — attach() accepts bare callbacks rather than a typed WebViewController, so it works with webview_flutter, flutter_inappwebview, or any future plugin. Adapt the integration glue (~6 lines) per your plugin of choice.

What happens when export fails​

FailureWhat Scout does
Network blip / 5xx / 429 / 408Exponential-backoff retry with full jitter (default 3 attempts, initial 1 s, max 30 s).
Retries exhausted, offlineBufferEnabled = trueBatch persisted to disk under the app's temp directory. Replayed on next initialize() and on app foreground.
Retries exhausted, offlineBufferEnabled = falseBatch dropped silently.
4xx (non-retryable)Batch dropped immediately so retry budget isn't burned on a permanent error.
Disk write fails (quota, permissions)Caught and swallowed; batch dropped.
App crash mid-writeThat batch is lost.

Running the example app​

The repo ships a runnable example at example/. For physical-device testing of the full diagnostic suite (UI hang, ANR, real SIGSEGV crash, WebView bridge) the flutter/samples/platform_design sample is a good starting point.

# iOS simulator
cd example
flutter run -d "iPhone 17"

# Android emulator / physical device
flutter run -d <device-id>

# For physical Android: reverse-forward your local collector
adb reverse tcp:34318 tcp:34318

Troubleshooting​

SymptomLikely cause + fix
ui_hang never fires on iOSiosHangThresholdMs: 0 disables it; check your config. Or the main thread genuinely isn't hanging — try a 300 ms while loop to confirm the watchdog is armed.
Two screen_view per navYou attached ScoutFlutter.navigatorObserver to both the root MaterialApp Navigator and a nested CupertinoTabView Navigator. That's correct — each Navigator emits its own screen_view. Filter dashboards by view.id to dedupe.
native_crash not appearing after iOS crashKSCrash writes asynchronously; the report drains on the next launch. Force-quit and relaunch the app, then check the collector log.
Android native_crash empty on API < 30ApplicationExitInfo requires API 30+. Older devices only get whatever the in-process NDK handler caught.
WebView spans not tagged span.source = webviewEither the embedded page isn't @base14/scout-react v0.1.5+ (no window.Scout), or your NavigationDelegate.onPageFinished is missing the injectShim(...) call.
Observer already has a Navigator assertionnavigatorObserver returns a fresh instance on every read, so attaching it to multiple Navigators is fine. If you hit this, you're caching one instance and reusing it — read ScoutFlutter.navigatorObserver afresh per Navigator.
HTTP requests not getting traceparentThe host isn't in firstPartyHosts. Add it explicitly (e.g. 'api.example.com') or use a wildcard ('*.example.com').
Crash button gives a graceful shutdown instead of SIGSEGVYou're calling exit(), which is graceful — no crash reporter intercepts it. Trigger a real fault instead (an uncaught error, or a native null-deref via your own platform-channel method).

Performance considerations​

  • Batched OTLP HTTP. Spans flush every 5 s (configurable). At default settings, telemetry overhead in normal use is 2–4 KB/s.
  • Disk-backed offline buffer. Worst-case disk footprint with default per-signal caps is ~25–35 MB. Lower the caps on low-end Android devices if needed.
  • Sampling. sessionSampleRate drops full sessions, never individual events — session traces stay coherent.
  • Async init. ScoutFlutter.initialize() is fire-and-forget. The app boot does not wait on it.

Security considerations​

  • PII scrubbing. Use beforeSend to redact attributes (event.remove('user.email')) or drop entire events (return null). It runs synchronously on every span / metric / log before export.
  • Custom headers for auth. Pass headers: {'Authorization': 'Bearer …'} to authenticate the OTLP export. Headers are sent on every request including offline-replay POSTs.
  • No telemetry-to-disk PII by default. The offline buffer writes the same OTLP JSON your live exporter would have sent — it doesn't add anything extra. If you don't want sensitive attrs on disk, scrub them in beforeSend before the batch hits the buffer.
  • TLS. Set secure: true (default) or pass an explicit https:// endpoint. No CA pinning by default; if you need it, wrap the outbound HTTP client yourself.

FAQ​

Does scout_flutter work on macOS / web / Linux / Windows desktop?

iOS and Android are fully supported, including native crash capture. macOS works for the Dart-side instrumentation (taps, navigation, HTTP, errors, lifecycle, logs) but the KSCrash / MetricKit / ApplicationExitInfo pipelines are mobile-only. Web works for Dart-side instrumentation — for richer web RUM, use @base14/scout-react directly in a web app and (for hybrid apps) bridge with the WebView bridge.

Will the SDK ever block my app's boot?

No. ScoutFlutter.initialize() is async and fire-and-forget — wrap it in unawaited(...) as shown above. If init fails (network down, disk full, etc.) the error is swallowed; your app keeps running.

How big are crash reports on the wire?

A KSCrash report with full register dump + callstack tree typically serializes to 30–80 KB. ApplicationExitInfo tombstones are capped at 32 KB. They're sent as part of the next launch's first batch.

Can I add custom spans?

Yes — the underlying OTel Tracer is accessible. Custom spans go through the same beforeSend / sampling / export pipeline as auto-instrumented ones.

Can I emit metrics or logs manually?

Yes:

ScoutFlutter.logInfo('checkout started', attributes: {'cart.size': 3});
ScoutFlutter.logError('payment failed', attributes: {'order.id': 'ord-1'});

// For an error with a stack trace, use reportError (emits an `error` span):
ScoutFlutter.reportError(e, st);

What's next​

References​

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