A long time ago, I wrote about a way to prettify JSON. It had the advantage that it didn't require you to load a heavyweight package such as js2-mode when all you wanted was to reformat some JSON in a reasonable way. The downside was that it called a Python module,
json.tool, to do the work. That's OK unless you don't have Python installed or don't want to shell out to an external process.
Now Wataru Miyaguni has an Elisp solution that doesn't require you to shell out to an external process. The json-reformat package reformats JSON into a standard format. If, like me, you don't write in JSON enough to justify use of one of the heavyweight JSON packages but nevertheless occasionally want to reformat JSON into a publishable format, this could be just what you need.