In the last two days I’ve written a new, simple JSON Formatter. This is a very simple tool that allows you to prettify/uglify JSON data. It is basically just a textarea tied to the JSON.stringify() method that is built-in on every modern browser.
I created this after being frustrated with other online formatters that don’t work well for large data because they require the data to be submitted to a server for validation. My tool runs entirely client side. Live preview here.