This is pretty cool. I still miss a Windows 3.1 word processor that had similar features. It allowed you to import any document of whatever length and then compare word length, sentence structure statistics etc. against your own writing and that of whatever you imported, including the Flesch–Kincaid scores. I like this Hemmingway app, too.
Just purchased the desktop version to play around with. Only $6.99. Hope I don't get infested with affiliate vermin, lol!