How to View File Extensions in OS X

This very short tutorial will show you how to determine the extension of any file on your Mac, and show you how to permantely have file extensions displayed in Finder, on your Desktop etc.

  1. By default, OS X doesn’t display a files “extension” – the part of the filename that typically follows a period (.) As you can see in the screenshot below, I have one folder and two files on my Desktop.
  2. os x desktop without file extensions displayed

  3. The fastest way to determine a file’s extension is to “right-click” the file (“Control + click” for single-button mouse folks) and select Get Info from the Options menu.
  4. Get Info on a file in OS X

  5. Expand the Name & Extension: section. Now you can see the extension. In the screenshot below you can see that the file has the extension of mp3.
  6. If you’d like to have the file extensions always displayed (although you can switch back at any time), close the Get Info window and launch Finder. Select Finder -> Preferences from the Menu Bar.
  7. os x finder menu bar with preferences highlighted

  8. Select the Advanced section and place a check in the box labeled Show all filename extensions and then close the Finder Preferences window.
  9. advanced section of the finder preferences

  10. Now when you view your files, their extensions will be displayed. As illustrated below, the same two files in the screenshot from back in step #1 now have their extensions displayed (mp3 and jpg respectively).
  11. a finder window with file extensions displayed

  12. That’s it! If you ever decide you don’t want to see the extensions, go back to the Advanced section of the Finder Preferences and remove that check mark.

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