Measure keyword density and spot over-optimization.
This checker counts how often a target keyword appears in text you paste and expresses it as a share of all words. The math is occurrences times the number of words in the keyword, divided by the total word count, times 100, shown to two decimal places. For a one-word keyword it counts whole words only, so "seo" will not match inside "seoprocheck". For a phrase it looks for that exact sequence of characters, which can match inside a longer word and misses the phrase when a line break separates its words. Plurals, synonyms and other variants are not counted. It all runs in your browser.
The label under the number comes from fixed thresholds in the code: below 0.5% is Too Low, above 2.5% is Too High (Keyword Stuffing Risk), and 0.5% to 2.5% is Good. The note under the result calls that range a rule of thumb for a primary keyword, not a target. That matches reality: Google has never published an ideal density, and its spam policies name keyword stuffing, meaning filling a page with repeated terms in ways that read unnaturally, as a violation.
Use a high number as a prompt to reread the copy aloud and replace forced repeats with pronouns or related terms. A low number is rarely a problem on its own if the page clearly covers the topic.