Before using a downloaded font in a Mac document, run Font Book’s validation and review its result: select an installed font and choose File > Validate Selection, or choose File > Validate File to check a font file before installing it. Green means passed, yellow means warning, and red means failed. Treat this as a check for font errors—not a guarantee that every character, style, or document will render as intended. Apple’s Font Book guide

Choose whether to validate the file or installed font

If you have not installed the font, open Font Book and choose File > Validate File. Browse to the font file and select it. This route lets you inspect the file before adding it to your Mac’s font collection. macOS supports TrueType (.ttf), Variable TrueType (.ttf), TrueType Collection (.ttc), OpenType and OpenType-SVG (.otf), and OpenType Collection (.ttc) formats. Apple says older suitcase TrueType and PostScript Type 1 LWFN fonts might work but aren’t recommended. Apple lists supported font formats and validation steps

If the font is already installed, select it in Font Book and choose File > Validate Selection. This is also the useful route when a font already in use looks wrong or a document reports a font-related problem. Installing a font through Font Book automatically checks it for errors and duplicates, but you can run validation later when you need to investigate a specific font. Apple’s install and validation instructions

Read the validation result and decide what to do

The Font Validation window assigns a status to each listed font: green for passed, yellow for warning, and red for failed. Click the disclosure arrow beside a font to inspect the details. If the list is long, use the pop-up menu at the top of the window to show Warnings or Errors. A warning is a reason to inspect the reported detail; it is not the same status as a failure. Apple documents the status icons and result filters

For a red failed result, review the details before deciding whether to keep the font. To remove a failed font from the validation window, select its checkbox and click Remove Checked. Confirm that you are removing the intended font, especially if the document depends on it. If you’re validating a file that has not been installed, do not assume a passing result means it has already been added for apps to use; Font Book’s guide separates validation from installation. Apple explains validation and removal

A green result means Font Book passed its validation check. It does not establish that the font contains every glyph you need, that a particular app will select the intended style, or that the layout will match on another Mac. Those are separate checks inferred from the scope of Font Book’s documented validation and preview features. After validation, confirm the characters, styles, and appearance that matter in your own document.

Check glyphs, styles, and the document itself

Before committing to a font, use Font Book’s preview to inspect the relevant characters and styles. In Font Book, select a collection or library in the sidebar, then use Grid to preview characters or see the font’s repertoire, Sample to enter your own sample text, or List to see available styles. The Info button can show details including language support, manufacturer, and the font file’s location. For a document with accented text, symbols, or a non-Latin script, enter representative text in the sample preview and look for missing or unexpected characters. Apple’s font preview guide

Then install the font if necessary and open the target document app to check actual text and layout. Look at the styles you will use, line breaks, and any important glyphs. This final app check is practical because Apple directs users to the developer for help when fonts do not appear in third-party apps such as Microsoft Word; Font Book validation alone cannot diagnose every app-specific issue. Apple’s Font Book troubleshooting guidance

If a font passes but still causes trouble

First check the validation details and verify that the intended style is available in Font Book’s List view. If the font appears more than once, use File > Resolve Duplicates to review copies. Font Book can resolve duplicates automatically or let you review them manually; in manual review, the recommended copy is marked “Active.” Avoid removing duplicate copies without checking which version you intend to keep. Apple’s duplicate-font instructions

If the font is missing from a third-party app, consult that app’s developer guidance. Apple notes that some fonts are activated automatically by macOS and cannot be deactivated or removed, so do not treat a dimmed Remove or Deactivate control as a validation failure. Use Font Book’s findings to identify font-file issues, preview tools to inspect glyph coverage and styles, and the document app itself to confirm the result you need. Apple’s troubleshooting guide

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