It is opened by default whenever the user clicks on a new .otf or .ttf font file. The user can view the font and install it, at which point the font will be copied to a centralised folder of user-installed fonts and be available for all apps to use.
It may also be used as a browser of all installed fonts. The user may view the list of fonts and see their alphabets, their complete repertoire of characters or how they set a sample text of the user's choice.
The program also allows users to:
- Group fonts into collections, which can then be used in all Cocoa programs.
- View details of fonts, such as their designer’s name.
- Activate/deactivate individual fonts or collections.
- Check the data integrity of font files.
- Export font collections for use on another computer
It does not feature any editing tools, even for changing font properties. This means that the user cannot use it to rename, merge or split up fonts or to redesign or modify fonts by (for example) changing kerning rules or exporting small capitals into a separate style.
In the 2003-7 period, Apple's Font Book faced some criticism regarding an inability to validate and auto-activate fonts. These features were added to Font Book with the release of Mac OS X Leopard.