Breakpoint overview

There is no user interface for editing breakpoints in Drupal 8. Due to the fact that breakpoints are defined in configuration files, it's not possible to provide a UI in contrib either.

Breakpoints are used to separate the height or width of viewports (screens, printers, and other media output types) into steps and provide for the case where a responsive design adjusts in order to display correctly on different devices. The Breakpoints module standardizes the use of breakpoints, and enables modules and themes to expose or use each others' breakpoints. The Breakpoint module keeps track of the height, width, and resolution breakpoints.

More detailed information about working with breakpoints and the breakpoint module can be found in the Working with breakpoints in Drupal 8 guide.