Apple - Use Quicklook to see the Content of .JSON files?

Download a release of qlstephen from Github, and load it into the /Library/Quicklook or ~/Library/QuickLook folder. Then, restart the Dock.

I use this all the time when previewing JSON files, and it works great.

also installable via

brew cask install qlstephen

You can use the quicklook-json plugin. If you want to install it via homebrew, run

brew cask install quicklook-json

which requires a running

brew install caskroom/cask/brew-cask

if you never did that before.