The keyword density checker is a tool for SEO to help determine now many times a keyword is used on a page within a site. This is useful to give an indicator as to whether a keyword is overused or underused.
While keyword denisty is not something that should be a main focus and not something Google has not really looked at since 2014, it nonethless can be very helpful to understand whether you are focussing enough on a keyword within your site as a general guide.
Learn more about keywords for SEO here.
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