Search engines are based on algorithms and despite all the artificial intelligence, they still have to rely on the content present on the website for ranking a website against keywords. And one of the clearest indicators of relevance of a web page to a keyword is the number of times a keyword is used on a webpage, also called keyword density.
And by using a keyword density tool you can yourself know the percentage of the total text on a web page used up by the keyword phrase.
There was a time when it was a clock work to rank websites by stuffing in keywords on a web page in a spammy way. However, search engines have grown up in intelligence and now also take in to account other signals regarding the quality of the content.
Therefore, it is now impossible to rank a webpage by using a keyword too many times on a webpage. Rather search engines now penalize such spammy and low quality content on websites. And a keyword density tool can help you to ensure that you do not use the keyword on your web page in a spammy way.
A keyword density tool also helps you to know that you have used a keyword enough number of times to send signal to the search engines about the topic or subject of the webpage.
There are many keyword density tools if you want to check the keyword density on your web page. Two of my favorite ones are:
All the above tools will give you a detailed report about different keywords phrases used on your web page and what percentage they comprise of the total text on page.
However, if you are using WordPress for your website, then you can use the WordPress SEO plugin by Yoast as the keyword density tool, though it does many other desirable things related to SEO too. It will give you keyword density right from within WordPress while you will be writing a post.You can also read about what is the best keyword density, if you want to know what percentage is best for SEO.