Json viewer for mac

You could use this add-on for Firefox : JSONView

Normally when encountering a JSON document (content type "application/json"), Firefox simply prompts you to download the file. With the JSONView extension, JSON documents are shown in the browser similar to how XML documents are shown. The document is formatted, highlighted, and arrays and objects can be collapsed. Even if the JSON document contains errors, JSONView will still show the raw text.

jsonpretty for pretty-printing JSON at the command line.

sudo gem install jsonpretty

If all you need is to be able to paste in text and see it prettily formatted with some basic "roll-up" functionality, try https://jsonformatter.org/json-parser.

Update: While trying out Olivier's new beta I responded to a feedback prompt, noting the lack of "roll-up" behavior for unnamed objects and arrays. He emailed me the next morning to say that he'd gone ahead and implemented that right away. Awesome!

You can use Jason as an offline app: http://www.macupdate.com/app/mac/35588/jason

If you want a JSON QuickLook viewer integrated into the Finder, you can try quick look JSON.