Troubleshooting Quick Look Extensions

Quick Look extensions can sometimes stop working due to conflicts with other installed apps. There are two common causes.

1. Multiple Quick Look extensions enabled for the same file type

You may not realize that some apps include their own Quick Look extensions. macOS enables them automatically, and they work quietly in the background.

For example, MarkEdit includes a Quick Look extension that adds syntax highlighting to Markdown files, but it doesn’t render a full preview the way Markdown Preview does. If both are enabled, macOS may choose the wrong one, and you won’t see the preview you expect.

To check which Quick Look extensions are active on your Mac, go to System Settings → General → Login Items & Extensions, scroll down to Extensions, select By Category, then look under Quick Look. From there you can disable any extensions you don’t need.

2. An installed app has declared a different UTI for the file type

macOS uses Uniform Type Identifiers (UTIs) to identify file types. App developers can declare custom UTIs for both new and existing file types, and many apps do this.

Quick Look extensions must declare in advance which UTIs they support. If another app on your Mac has registered a custom UTI for a file type, the Quick Look extension may not recognize it, and macOS won’t be able to connect the file to the extension.

To fix this, we need to know which UTI your Mac is using for the file. We’ve built a small utility called UTI Finder to make this easy — it’s bundled with all of our Quick Look extension apps.

To use it, open the Help menu in the app and launch UTI Finder. Select the file that isn’t previewing correctly, copy the result, and send it to us. We’ll include the UTI in the next update.