OS X includes the json_pp command, so I often just do this to format JSON in my clipboard:
pbpaste | json_pp | pbcopy
For just viewing, I like Node's console.dir() formatting better since it's more compact and colored (but it's unquoted JS objects, not JSON), so I aliased this command in my shell:
One of my absolute musts in a text editor is a feature that prompts for a command, pipes the selected text into it and replaces it with the command's output (for Visual Studio Code it comes as a plugin). So "Ctrl+A, Ctrl+\, 'json_pp', Enter" and voila, formatted JSON in my editor (Ctrl+\ is what the command is bound to). Also works great with grep, sort, awk...
jq is freaking awesome! It can do amazing stuff, it's like awk for JSON on steroids. Highly recommend reading the documentation: https://stedolan.github.io/jq/manual/