The macOS Quick Look system, which provides quick previews of files when you hit Space in the Finder, as well as tiny preview thumbnails on icons in the Finder, is extendable by third-party applications for file types for which the Mac does not natively provide Quick Look support.

Nova takes advantage of this by providing two Quick Look extensions: Previewing and Thumbnailing.

The Previewing extension provides support to macOS for displaying syntax-highlighted code in the preview when you select a file type that Nova supports in the Finder and hit Space. This syntax-highlighting is only performed on-demand, at the moment that you preview the file.

The Thumbnailing extension provides support to macOS for adding code thumbnails to icons in the Finder for the file types that Nova supports. This process is invoked automatically by macOS at various times in the background when the system decides that a folder needs its cache of Quick Look thumbnails updated. When this happens, this can cause the Nova Quick Look Thumbnailing service to appear in Activity Monitor for a few minutes as the system requests thumbnails for files.

If you notice that the Thumbnailing extension is appearing more often than you’d like, or if you decide you don’t need code previews in icon thumbnails, you can disable this service system-wide by doing the following:

  1. Open System Preferences
  2. Click “Extensions”
  3. From the list of extension services on the left, click “Quick Look”
  4. In the list on the right, uncheck Nova’s “Quick Look Previewing” and “Quick Look Thumbnailing” extensions

This article was last updated on January 19, 2021