Tool for Determining Unicode Ranges in Use on a Page

I've had a bit of a look around but none of my searches found much - does anybody know of a good tool (potentially a bookmarklet) that can take a page and tell you the ranges of Unicode currently in use on it? A bonus feature would be the ability to parse the exact characters in use to a useful small range or couple of ranges that would cover all characters in use.

I'm in the process of subsetting our web fonts for optimised loading using the CSS unicode-range option and it occurred to me that it'd be helpful to be able to analyse a site properly instead of just relying on a kind of vague 'Latin / Extended / Cyrillic / Eastern Asian / Other' character breakdown.