Apple Diagnostics

Apple Diagnostics is a troubleshooting utility for Macs. The current version comes pre-installed with macOS Big Sur (version 11) or later.

Usage
When running the software, it presents a progress bar similar to that shown when recent versions of macOS are booting. The vary basic user interface simply identifies any issues that may have been found, along with a reference code and the serial number of the Mac that can be shared with Apple Support staff.

History
In 2013, Apple Diagnostics succeeded Apple Hardware Test (AHT), which was first released on CD-ROM for Open Firmware Macs produced in 2000 or later.