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Frame Jank Visualizer

Drop in a Flutter frame's raster stats to see which layers made it slow.

Source

When a Flutter frame janks, the question is which layer was expensive to rasterize. The Flutter engine can re-render the last frame with raster stats: for every layer, how long it took to rasterize and a PNG snapshot of what it drew. frame-profiler-vmservice-cli connects to a running app’s VM service, calls _flutter.renderFrameWithRasterStats, and writes the result to a JSON file:

dart ./bin/vmservice_cli.dart ws://127.0.0.1:39255/_E1uPHKfjI8=/ws ~/Downloads/flutter-frame-log.json

Drop that file below to see each layer, slowest first. Nothing leaves your browser.