Disk First Aid


Disk First Aid is a free software utility made by Apple Inc. that was bundled with all computers running the classic Mac OS. This tool verifies and repairs a limited number of directory structure problems on any HFS or HFS Plus hard disk or volume.
Disk First Aid is a very simple tool, with it only being able to detect and repair directory damage and many books are critical of its sometimes inaccurate reporting of errors, and often suggest to run the tool more than once to ensure you are receiving a consistent result. Disk First Aid is located in Applications:Utilities:Disk First Aid. The classic Mac OS provides an option to run Disk First Aid on startup, although it has been reported that it provides little gain and sometimes can amplify a problem.
Its capabilities were incorporated into Disk Utility in macOS.

Situations to use the tool

One source suggests that disk utility should be used when there are:
as well as for general maintenance every 6 months.

Analysis

Disk First Aid has built-in capabilities to check for damage to:
After analyzing the disk directory, Disk First Aid determines whether it is able to repair any damage that was detected. The utility can commonly only fix problems associated with the catalog/extents files and the volume bitmap. Commonly, the program reports that there is an error, but cannot fix it.