Disk Utility is Apple's go-to macOS app for finding and repairing common disk errors, but if it's your Mac's internal disk that's the problem, then your Mac might not even start up into macOS.

You are about to transfer some important files from an external drive to your Mac, and suddenly you get the message “Disk Not Ejected Properly” The transfer fails, and you have to start all over again ...

The First Aid feature in Apple’s Disk Utility (/Applications/Utilities) represents one of the oldest and most helpful repair utilities available for your Mac. But ...