Perf Monitor

Watch performance on a real device. The Perf Monitor is a live on-device HUD showing FPS, jank, CPU, and memory while you use the app — streamed to the Buoy Desktop dashboard so you can watch it full-size while you drive the phone.

measure it, in 73 seconds

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The film and the demo show the React Native tool, and the demo uses mock data. Use the Flutter setup and feature descriptions below for supported behavior; the demo does not establish Flutter feature parity.

Installation

The monitor is implemented in Dart. Restart the app after adding the package or registration. Using the buoy umbrella? It's already registered. Standalone:

import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:buoy_perf_monitor/buoy_perf_monitor.dart';

void main() {
  if (kDebugMode) registerBuoyPerfMonitor();
  runApp(const MyApp());
}

import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:buoy_perf_monitor/buoy_perf_monitor.dart';

void main() {
  if (kDebugMode) registerBuoyPerfMonitor();
  runApp(const MyApp());
}

Open the PERF tool from the floating dial to see live metrics and toggle the HUD.

What It Measures

Use a debug build with the widget mounted. These measurements include debug-mode overhead; do not present them as release-build performance. Repeat the same interaction when comparing changes.

• FPS + jank — from SchedulerBinding.addTimingsCallback: build (Dart UI thread) and raster (GPU thread) frame timings. FPS is activity-gated: an idle Flutter app renders no frames, so the HUD shows — at rest — because no active frame rate is available.
• Memory (RSS) — from dart:io's ProcessInfo.currentRss, sampled continuously even while the UI is still.
• CPU — from /proc/self/stat on Android (no pure-Dart source exists on iOS yet).

Coming Soon

Benchmarking and batch reports — recorded, comparable runs with ranked reports, like the React Native Bench tool — plus Dart Top, a "what's eating the thread" profiler. Vote on the roadmap.

What's Next

• Buoy Desktop — Watch the live HUD full-size on your desktop
• Events Timeline — Performance in context with everything else
• Network Monitor — Find the slow requests behind the jank

FAQ

How do I measure FPS and jank in a Flutter app on a real device?

Add buoy_perf_monitor and call registerBuoyPerfMonitor() — a live on-device HUD reports build (Dart UI thread) and raster (GPU thread) frame timings from SchedulerBinding.addTimingsCallback, plus memory (RSS) and, on Android, CPU. It streams to Buoy Desktop so you can watch it full-size while you drive the phone.

Why does FPS show a dash when the app is idle?

FPS is activity-gated. An idle Flutter app renders no frames, so the HUD shows — at rest because there are no new frames to measure.

Does it need native code?

No — it's pure Dart. No native libraries, no FFI, no platform channels, and no rebuild.