Jsoneditor
Switch editor mode using the mode box.
Note that the mode can be changed programmatically as well using the method
editor.setMode(mode), try it in the console of your browser.
Others: 1. http://jsonviewer.jaycodesign.co.nz/ 2. http://jsbeautifier.org/ 3. http://marianoguerra.github.io/json.human.js/