Web - Master / Designer Tools - Count
Keyword Density of Web Pages
The tool counts the absolute number and percent (density) of usage of words - single words, combinations of two words and combinations of three - in the indicated web page.
The results are useful to determine the relevance of your keywords, as indicated by you in your keyword metatag, within your web page by analyzing this words density.
The results also very useful to find out the relevant keywords within a plain text you prepare not specifically for Internet.