The keyword density is the percental frequency of single keywords or multiple word phrases in the content of a single web page. It is the relation between the count of a keyword or keyphrase and the total number of words or phrases used on a specific page. In the course of the evaluation of a page, search engines are using the density as a clue whether a page is relevant for a given keyword or keyphrase or not. Even though this is only one of many factors for classifying a page, it has a high-impact on the reachable position of a page in the search results. If the keywords or phrases are distributed in the content, the page is potentially ranked on a higher position.
If you are using wordpress for blogging you can install our keyword statistics plugin for wordpress. It comes with the same density analyzer tool which is used by the bookmarklet and can be used to integrate the keyword density checker into the content generation process. Besides that, the plugin can automatically generate the appropriate meta informations for keywords and many other things.
Those already using other SEO plugins for metadata generation may have a look at the keyword density checker. With this plugin you can have a look at the used keywords but it does not generate any meta informations except of a keyword meta suggestion which can be used to copy the calculated ones into other SEO plugins input fields for the meta keywords. The keyword density checker in only running at post-edit and page-edit dialog at the backend of administrators and authors. On ordinary page requests no extra code has to be executed.