The modest writing is not as modest as you might think, especially on a Mac. Fonts are more plug-ins than you imagine, and since they are loaded by macOS and the apps running on them, bad fonts can have unexpected consequences.
These consequences can be seen by the relatively harmless How some characters are displayed incorrectly, something more annoying, like apps that refuse to load, or features that no longer function as they used to. Faulty fonts are rarely the cause of problems with the macOS system, but if you have problems that make no sense, reading your fonts is a good first step for troubleshooting.
Luckily, Apple includes a tool to install, validate, and troubleshoot common fonts with every Mac. If your Mac does not behave properly the next time and you have no more ideas, checking your fonts is a good troubleshooting step.
How to Check Fonts on a Mac
First, open the Font Book App. You can find it in your application folder. (Open the Finder and click Go> Applications to open the folder.) After opening, select all of your fonts by clicking one and pressing Cmd + A.
] Right-click one of the fonts and click "Check Fonts."
When the review is complete, a new window will appear confirming if any of the fonts are present. Your bugs are corrupted. A green icon indicates that they are OK, a yellow icon indicates that there are warnings about the font, and a red icon indicates that the verification failed.
How to remove corrupt or duplicate fonts
If one of your fonts is actually damaged, select the check boxes next to it and click the "Remove Ticked" button.
. The selected fonts will be removed from your system. If this is actually required, restart your Mac after the fonts have been removed.