Breakpoints are utility configurations for other modules. Breakpoints can be loaded using the breakpoint manager service and by specifying a group. For example, the following code returns all breakpoints used by the Toolbar module:

\Drupal::service('breakpoint.manager')->getBreakpointsByGroup('toolbar');

This code invokes the Drupal container to return the service to manage breakpoints, which, by default, is \Drupal\breakpoint\BreakpointManager. The getBreakpointsByGroup method returns all breakpoints within a group, which are initiated as the \Drupal\breakpoint\BreakpointInterface objects.

The Toolbar element class utilizes this workflow to push the breakpoint media query values as JavaScript settings for the JavaScript model to interact with.