What is it?

The Flutter widget inspector is a powerful tool for visualizing and
exploring Flutter widget trees. The Flutter framework uses widgets
as the core building block for anything from controls
(such as text, buttons, and toggles),
to layout (such as centering, padding, rows, and columns).
The inspector helps you visualize and explore Flutter widget
trees, and can be used for the following:

understanding existing layouts

diagnosing layout issues

Get started

To debug a layout issue, run the app in debug mode and
open the inspector by clicking the Flutter Inspector
tab on the DevTools toolbar.

Note:
  You can still access the Flutter inspector directly from
  Android Studio/IntelliJ, but you might prefer the
  more spacious view when running it from DevTools
  in a browser.

Debugging layout issues visually