Flesch reading ease in Yoast: what the number measures

Where the score went in Yoast SEO

For years Flesch reading ease was one of the traffic lights in Yoast's readability analysis. In version 19.3, Yoast moved it to the Insights tab, next to word count and reading time, and stopped using it in the readability score. Yoast's explanation was that the number is hard to act on: it tells you a text is difficult without telling you which part.

Its replacement in the readability analysis, Word complexity, is a Premium assessment. It highlights words Yoast considers complex and turns orange when more than 10 percent of the words in the text fall into that group. Word forms of your keyphrase are excluded, so you are not penalized for the topic's own vocabulary.

The formula was designed for English. Yoast has noted that it is less reliable in other languages, so treat the number with extra caution if you write in one.

Rudolf Flesch's 1948 formula

The score comes from Rudolf Flesch, who published it in 1948 as a way to estimate how hard a passage is to read. Yoast gives the formula as:

206.835 - (1.015 x average sentence length) - (84.6 x average syllables per word)

Long sentences and long words push the score down. Yoast's guidance maps the result to reading levels like this:

A related measure, the Flesch-Kincaid grade level, turns the same inputs into a school grade. Yoast shows reading ease.

What the number can and cannot measure

Because it only counts syllables and sentence length, the formula has well-known blind spots:

• Nonsense can score well. "The cat sat. It was red. We ran." scores as very easy and says nothing.
• Necessary terms score badly. A guide to "authentication" or "photosynthesis" loses points for words its readers already know.
• Structure is invisible. Headings, lists, tables and examples make a page easier to use, but the formula cannot see them.
• Meaning is invisible. A clear sentence with one long word can score worse than a vague sentence made of short ones.

So a low score on a page for specialists may be exactly right. A low score on a page for beginners, such as a setup guide or a product FAQ, is a better reason to revise.

Raising the score without talking down

If the score is lower than your audience warrants, the formula tells you where to look: sentence length first, word length second.

1. Split long sentences. Any sentence with two "and" or "which" clauses can usually become two sentences.
2. Swap long words for plain ones only when they mean the same thing. "Use" for "utilize", "help" for "facilitate", "about" for "approximately".
3. Keep the technical word, and define it once. "Latency, the delay before a response starts" costs a few points and saves the reader a search.
4. Move detail into lists. A sentence listing five items reads better as five bullets.

Read the passage aloud after editing. If it sounds choppy, you went too far; mix short sentences with medium ones.

Readability does not feed rankings directly. Its effect is on people: whether they understand the page, stay on it and do what they came to do.

Readability scoring in Hydrogen SEO

Hydrogen SEO uses a simpler readability measure in its SEO score: the average number of words per sentence, with no syllable counting. The readability part is worth 20 points minus 0.4 for every word in the average sentence, so an average of 15 words scores 14 points and 25 words scores 10. Like Yoast's traffic lights, it is a prompt to review, not a target.