Paste your text, add the keyword, and see how often it appears, its density as a percentage, and the twenty words you use most.
Paste the article or page text into the box and type the keyword you are targeting. Press Calculate. The top number is the keyword's density, with a verdict next to it, and the table below lists your twenty most frequent words with a bar for each. If the keyword sits above 2.5 percent, cut a few mentions or replace them with related terms from the LSI keyword generator. If it is under 0.5 percent, add it where it reads naturally, starting with the introduction and a heading.
There is no magic percentage, but there are two ways to lose: a keyword that barely appears on a page that is supposed to rank for it, and a keyword repeated so often that Google's spam systems and your readers both notice. Density gives you a fast read on which side you are on, and the frequency table shows whether the page is really about the topic or drifting into something else.
Somewhere between 0.5 and 2.5 percent for the main keyword covers most pages. Above that, rewrite. The related terms matter as much as the exact phrase, so count those too.
As a signal, barely. As a diagnostic, yes. Google ranks on meaning, but a page that never says its keyword rarely ranks for it, and a page that repeats it every sentence reads as spam to people and machines alike.
It counts whatever you paste. Paste the visible text of the page, including headings, for a realistic number. Alt text is not visible, so leave it out.