Meta keyword creator

Looking for an extension that looks through the text in the page you are editing and finds the most common words, and then puts the top 5-10 in a keyword meta tag. 

The keyword generator extension would look through the text in the page you are editing and finds the most common words, and then put the top 5-10 in a keyword meta tag.

I've got hundreds of pages that all need keywords, and it is very annoying having to do a quick read of the document, pick out the keywords manually and paste them into the meta tag myself.

There is an online tool called "Keyword Density Analyzer & META Tag Creator" that does something similar to what I'm talking about.

It scans through your page, then lists the top keywords, and you can pick and choose what keywords you want in the resulting meta tag.

An extension that mimics that page would be brilliant.