3D Printing/Modeling, Woodworking, Coding and generally making stuff

QuickLook - MacOS


QuickLook is the tool that Finder uses in MacOS to provide previews of file contents when pressing space bar on a file in Finder. qlmanage is the command line tool used to administer QuickLook.


Use qlmanage to diagnose and change QuickLook settings.

Usage: qlmanage [OPTIONS] path...
        -h              Display this help
        -r              Force reloading Generators list
        -r cache        Reset thumbnail disk cache
        -m [name ...]   Display statistics about quicklookd. Stats names:
                        * plugins       Show the generators list
                        * server        Show quicklookd life information
                        * memory        Show quicklookd memory consumption
                        * burst         Show statistics about the last burst
                        * threads       Show concurrent accesses stats
                        * other         Show other information about quicklookd
        -p              Compute previews of the documents
        -t              Compute thumbnails of the documents
        -x              Use quicklookd (remote computation)
        -i              Compute thumbnail in icon mode
        -s size         Size for the thumbnail
        -f factor       Scale factor for the thumbnail
        -F factor       Scale factor for the thumbnail, draw downscaled and compare to 1x
        -z              Display generation performance info (don't display thumbnails)
        -o dir          Output result in dir (don't display thumbnails or previews)
        -c contentType  Force the content type used for the documents
        -g generator    Force the generator to use

To find the QuickLook generator for a specific file extension:

qlmanage -m | grep "md"

To test a quicklook generator run it explicitly on a file you want to view. For example:

qlmanage -p /path/to/sample/file.ext

Unsigned QuickLook Generators

In more recent versions of MacOS (Mohave, Big Sur, etc...) new security requirements have been put in place. This means a number of older QuickLook generators are not signed and so do not work without approval. To approve the extensions you must do the following:

  1. Install the QuickLook generator, e.g. brew install qlcolorcode
  2. On your terminal, xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator run (using sudo if needed), replacing QLColorcode with whatever the name of the QuickLook plugin
  3. Reload the QL Generator with qlmanage -r
  4. Now refresh the cache qlmanage -r cache
  5. Restart Finder by running killall Finder

For those wanting to cut and paste the whole lot:

brew install qlcolorcode
xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator
qlmanage -r
qlmanage -r cache
killall Finder

QuickLook Generators I use

brew install qlstephen qlcolorcode qlmarkdown
xattr -cr ~/Library/QuickLook/QLMarkdown.qlgenerator 
xattr -cr ~/Library/QuickLook/QLStephen.qlgenerator 
xattr -cr ~/Library/QuickLook/QLColorCode.qlgenerator
qlmanage -r
qlmanage -r cache

Adding support for unknown file types

If there is a file extension that is not being shown by any of your QuickLook extensions, you can easily add them to the list of one of the ones I showed above.

For example, to add .conf files to the QLColorCode extension do the following:

  1. Find an example file of the type that you want to add to QuickLook

  2. Run mdls -name kMDItemContentType followed by the file name so in my case:

    mdls -name kMDItemContentType /Users/me/wpa_supplicant.conf
  3. Make note of the output. In my exmaple this was:

    kMDItemContentType = "dyn.ah62d4rv4ge80g55sq2"
  4. Now you need to add the part in quotes to the QL config. So:

    nano ~/Library/QuickLook/QLColorCode.qlgenerator/Contents/Info.plist

    where QLColorCode is the QL generator I want to add this file to.

  5. In the editor you just opened, look for three lines that look like this:

  6. Now add a new line before those that includes the part in quotes from step #3, so:

  7. Press CTRL-X and then y and Enter to save the file

  8. Run

    qlmanage -r
  9. You may need to restart Finder

    killall Finder

Now you can press space on the new file type and it should open in QuickLook for you.

October 1, 2021 (3y ago)