As often as Quick Look is among the tips I share with clients, I’m stunned that I haven’t written a post about it until now. In fact, in nearly six years, it got only a single mention: five years ago in Command Day.
Quick Look is a feature of macOS that has been around since 2007 and sports the simplest keyboard shortcut: the Space Bar.
The beauty is that you can view the contents of a file without having to open it in a separate application. This saves you the trouble of closing the item and switching back to the application where you found it in the first place.
Get a Quick Look
To preview many types of items, simply click an item and tap the Space Bar. macOS provides built-in support for common document formats like iWork, Microsoft Office, PDF; image files like JPEG, PNG, GIF; audio and video formats that are natively supported; and more.
While viewing a Quick Look window, you may find options on the toolbar to make the window full screen, annotate a document, rotate an image, trim a song or movie, share the item, and open the item in its default application. See Apple’s full list. You can also select text in a document that contains it and resize the window as you wish.
In the Finder, Quick Look operates on one or more selected files. It also works on attachments in Mail and Messages. Oddly, when multi-selecting in the Finder, the initial item that appears is consistently the last you selected rather than the first. You can cycle through selected items using the Right and Left arrow keys.
To dismiss a preview, you may be tempted to click the 
in the top left corner. However, I think you’ll find it faster to just tap the Space Bar again.
Start Full Screen
To instantly open a preview in full screen, I just learned that the Finder supports Option+Space. In full screen, you can page through a multipage PDF or other document using the spacebar. Press Escape to close the preview.
Additionally, select multiple items of one or more kinds and use Option+Space to present a playable slideshow. However, this does not display more than the first page of any document.
Quick Look in the Dock
When you put a folder in the Dock, it operates a little differently from the Finder. You can choose to display the contents as a Fan, Grid, or List, and can only interact with one item at a time, such as opening a document or moving it to the trash.
In Grid view, you can mouse over an item and tap the Space Bar to show a Quick Look popover window.
Advanced Navigation
While in a Finder window, you can activate Quick Look and then use the arrow keys to navigate among the items in the window. The preview window will update as other files are selected, even if you cannot see the selection in the window.
For example, in a List view, you can move the selection with the Up and Down arrow keys. Also, if items listed are not in Groups (thus, disclosure triangles appear next to folders), you can also open a folder with Right and close a folder with Left.
You can extend Quick Look’s capabilities with any number of plugins, such as those mentioned in this Wired article. For example, plugins can list the contents of a folder or of a compressed file, show metadata for third-party video files, and peer into all manner of coding languages.
There are plenty of free Quick Look plugins as well as paid apps like Peek that offer support for hundreds more file types. Just search for “Quick Look” and the name of the application whose files you want to preview. If you need help installing a plugin, let me know.
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