Resolve Font Book Duplicates and Check Corrupt Fonts Safely
Font Book can validate damaged fonts and resolve duplicates. Inspect the affected family and active copy first; do not remove system fonts blindly.
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If a document shows boxes or only one app substitutes a typeface, start by checking the font’s state and duplicates in Font Book. Apple documents validation and duplicate-resolution tools in the app. They help narrow down a font-file problem, but do not guarantee a fix for every application’s rendering behavior.
Validate the font file
Select the suspect font and choose File > Validate Selection, or choose File > Validate File to inspect a font file in Finder. Apple’s validation window marks a pass in green, a warning in yellow, and a failure in red. Expand the details to identify the affected file, then decide whether the failed font should be removed. Keeping the original download or installer can make restoration easier.
Compare duplicate copies before resolving them
Choose File > Resolve Duplicates and select automatic or manual handling. In manual mode, compare the copies and note the one Font Book labels Active. Depending on settings, automatic resolution may deactivate duplicates or move them to Trash. Review those settings and the family selected before applying a change. Removing a family without checking its scope can affect more than one copy.
When the problem appears in only one app
If the same font works elsewhere, check the document’s embedded fonts, the app’s own font handling, and app updates before changing the system-wide collection. Apple directs users with problems in third-party apps such as Word to the app developer. Font-management author Sharon Zardetto’s 2006 Mac OS X article also warns that removing a family can affect several copies; it is historical caution, not current macOS menu or system-font guidance.
Expert perspective
Zardetto’s specialist font-management writing highlights how a duplicate’s removal scope can be easy to misread. Treat the 2006 material as a caution about selection scope only. Follow Apple’s current steps for the interface, avoid deleting system fonts or caches directly, and use the affected app developer’s current instructions when the issue is app-specific.