Start an application to debug

Next, start an app to connect to.
This can be either a Flutter application
or a Dart command-line application.
The command below specifies a Flutter app:

You need to have a device connected, or a simulator open,
for flutter run to work. Once the app starts, you’ll see a
message in your terminal that looks like the following:

Open the DevTools instance connected to your app
by opening the second link in Chrome.

This URL contains a security token, 
so it’s different for each run of your app. 
This means that if you stop your application and re-run it, 
you need to connect to DevTools again with the new URL.

Connect to a new app instance

If your app stops running
or you opened DevTools manually,
you should see a Connect dialog: