Why Keyword Density Is a Weak, Outdated SEO Signal
Keyword density — the percentage of a text's words that match a target keyword — was a meaningful ranking signal in the very early era of search engines, when algorithms had limited ability to understand context and relied heavily on simple term frequency. Modern search engines use vastly more sophisticated relevance signals (semantic understanding, entity recognition, user engagement data) and no longer reward hitting a specific density percentage — in fact, artificially inflating keyword repetition to hit a target density is now more likely to read as spam (keyword stuffing) than to help rankings at all.
Readability scores (like Flesch Reading Ease) measure something more durably useful: sentence length and word complexity, which correlate with how easy content actually is for a human to read and understand — a genuinely helpful signal for content quality regardless of what search algorithms reward at any given moment, since content people can't easily read tends to perform poorly regardless of its keyword optimization.
The practical takeaway most current SEO guidance converges on: write for genuine readability and comprehensive coverage of a topic, use a keyword naturally where it fits, and treat any specific density percentage target as a legacy heuristic rather than a real modern ranking lever.