"keyword" seems a small word but it is a big factor in ranking highest in search engines. In the starting era of the internet the density of keywords haven't had the limitations. So people started stuffing keywords in their websites to make website appear on the first position in search engines. But now ranking website with keywords is not that easy.
Mentioning your keyword for specific times (Careful! Not too much, not too less), in your website, will send search engine the signals that your website has the content related to that particular keyword.
Now we know it is important to check the keyword density in your article, but do you want to waste time on calculating keywords in your article? Absolutely not! That is why SEO Tools Best brought Keyword Density Checker only for you to save your time.