Readability checker (Flesch, Flesch–Kincaid, Fog)
Readability formulas estimate how hard a text is to follow from sentence length and word length. They do not judge quality or meaning (a beautiful paragraph can score badly), but they are a fast, repeatable way to check whether your writing matches its audience.
What the formulas measure
Flesch reading ease scores 0–100 from words per sentence and syllables per word; 60–70 is plain English and most newspapers sit there. Flesch–Kincaid converts the same inputs into a US school grade. Gunning fog adds a penalty for words of three or more syllables and returns the years of schooling a reader needs.
What the score cannot tell you
None of these formulas read for sense, structure or accuracy, and none of them is an AI detector. A text can be perfectly readable and still be flagged, or unreadable and pass. Use readability to fit the audience; use the detector to see how a classifier reads your rhythm; use your own judgement for everything else.
Targets that work
General web copy: ease 60+, grade 7–9. Academic writing: grade 12–15 is normal, but each sentence should still carry one idea. Emails: grade 8 or below gets answered faster. Marketing: grade 6–8 and short paragraphs. Non-native readers: prefer ease above 65 and sentences under 20 words.
Is a higher Flesch score always better?
No. It means easier, not better. A legal notice at grade 6 may lose precision; a children's story at grade 14 will lose its readers. Match the audience.
Do readability scores affect AI-detector results?
Indirectly. Detectors respond to uniform sentence length and predictable word choice, which also move readability scores. The sentence-variety tool shows that rhythm directly.
How accurate is the syllable count?
It is estimated from spelling patterns, which is how the original formulas were computed by hand. Expect small errors on names and unusual words; they rarely move the grade by more than a fraction.