Keyword density checker is a tool used in search engine optimization (SEO) to measure the frequency of keywords on a web page. It calculates the percentage of times a keyword appears in the content compared to the total number of words on the page. Keyword density is an important factor in SEO because it helps search engines determine the relevance of a web page for a particular keyword or topic. A keyword density checker can be used to analyze a web page and identify whether the keyword is used too frequently or not enough. Overusing keywords can result in a website being penalized by search engines for keyword stuffing. On the other hand, not using keywords enough can result in the page being considered irrelevant for the topic. A keyword density checker can help website owners and SEO professionals optimize their content for search engines by ensuring that they use keywords in a way that is natural and relevant to the content.