What are flutter_jank_metrics_<num>.json files in Flutter project?

What are flutter_jank_metrics_.json in Flutter project root folders? Why & How they generated?

It might related to Flutter UI janky, but I don't see it on Flutter's official document.

Solution

For future me and people who are also curious.

The jank file are from the interacting-terminal after flutter run, you can press j to generate it.

j Dump frame raster stats for the current frame. (Unsupported for web)