A good, free text editor is Notepad++. You may use it as it is, or you may download an additional plugin, JSToolNpp, which is quite useful with Strive for Power. First, install Notepad++; then extract the JSMinNPP.dll addon and put it into the "plugins" directory. Once you've restarted Notepad++, click Plugins -> JSTool -> JSformat to format your save as a tree.
Alternative solution for people who don't want to install additional software: jsoneditoronline.org
(it's preposterous that Wordpad can't save in UTF-8 format, while even Notepad can)