Keyword Density Checker

Keyword density measures how often a term appears relative to the total number of words on a page. The counting model is raw term frequency— the literal number of times a token occurs — defined in Manning, Raghavan & Schütze's Introduction to Information Retrieval (Cambridge, 2008). The density percentage itself uses the formula documented by Yoast SEO:

density = (keyphrase count ÷ total words) × 100

The tool runs entirely client-side in four deterministic steps:

1. Normalise.The text is lowercased and every run of non-alphanumeric characters is replaced with a single space, keeping intra-word apostrophes and hyphens so “co-op” and “don't” stay intact.
2. Tokenise. The normalised text is split on spaces into a word array. Its length is the total words — the denominator for every density figure.
3. Count. For single words, each unique token is tallied. For 2- and 3-word phrases, a sliding window walks every contiguous sequence and counts exact matches. Density is each count divided by total words.
4. Grade the focus keyphrase. If you enter one, its exact occurrences are counted and mapped to a band: under 0.5% (under-used), 0.5%–3% (healthy), or above 3% (stuffing risk).

The healthy 0.5%–3% band comes from Yoast's keyphrase-density guidance; the upper warning aligns with Google Search Central's keyword-stuffing policy, which treats cramming a page with keywords to manipulate rankings as spam. When “ignore common words” is on, stop words (the, a, of, to, and…) are hidden from the table, but they are never removed from the total-word denominator — so densities stay comparable to what a search engine actually measures.

For credibility the focus keyphrase is counted two independent ways: a sliding token window and a separate text scan. If the two ever disagree, the tool shows a warning instead of a silent number — the same dual-method check the site's tax calculator uses against the IRD formula.

• Yoast SEO — Keyphrase density: the golden mean (formula + 0.5%–3% band)
• Google Search Central — Spam policies: Keyword stuffing
• Manning, Raghavan & Schütze — Introduction to Information Retrieval, Ch. 6 (term frequency)

The keyphrase-density formula and the healthy 0.5%–3% band on this page were last reconciled against the Yoast and Google Search Central sources on 2026-06-24.