Paste any text to get the standard readability scores — Flesch, grade level, Fog, SMOG, Coleman-Liau and ARI — plus an honest note on what scores cannot measure.
All standard formulas are computed from the same counts: words, sentences, syllables, characters and complex words (three or more syllables). Flesch Reading Ease runs from 0 to 100 with higher meaning easier; the grade-level formulas estimate US school grades. Scores are best used to compare drafts of the same document, not as an absolute quality judgement — a low score can be appropriate for a technical audience, and a high score does not make a text correct.
Which score matters most? Flesch Reading Ease and Flesch-Kincaid Grade are the most widely reported. SMOG is often preferred for health and public information because it was validated for comprehension.
Why do two checkers give different numbers? Syllable counting is an estimate, and tools differ on handling numbers, abbreviations and sentence fragments. Small differences of a point or two are normal.
How much text is needed for a reliable score? At least 100 words, and ideally 300 or more. SMOG was designed around 30 sentences, so very short samples make it unstable.