Keyword density checker tool
Free keyword density analyzer tool - allows you to find words and phrases density in the text.
Semantic analysis, the number of occurrences of each word and combinations of 2, 3, 4, 5 words. Find keywords in your text/article.
Optimal number of words to use for a website
You should not optimize one page for a large number of keywords, namely, more than 3-5 words. But at the same time, each keyword should be maximally disclosed in the text. Collect keyword statistics, analyze them to understand what people are actually looking for when they enter this query and answer all the most closely related subqueries with the given keyword. In this case, your text will be the most relevant to the main keyword.