Readability Checker
Score your writing on Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog and SMOG. Highlight long sentences and passive voice in seconds.
How each formula works
Flesch Reading Ease rates text from 0 (extremely hard) to 100 (extremely easy). It weighs average sentence length and average syllables per word. A score of 60 to 70 is the sweet spot for plain English; 30 or below reads like a legal contract.
Flesch-Kincaid Grade Level translates the same inputs into a U.S. school-grade number. A grade of 8 means an average eighth-grader can read it comfortably. Most consumer copy aims for grade 6 to 8.
Gunning Fog approximates the years of formal education a reader needs. It combines sentence length with the percentage of complex words (three syllables or more). Newspapers target a Fog index of 8 to 12.
SMOG (Simple Measure of Gobbledygook) was designed for evaluating health and safety materials. It counts polysyllabic words across 30 sentences and is generally considered the most conservative of the four — it tends to score harder than Flesch-Kincaid.
Target ranges per audience
- Consumer marketing, news, product pages — grade 6 to 8. Flesch Reading Ease around 60 to 80.
- Technical documentation, B2B blog posts — grade 8 to 12. Flesch Reading Ease around 50 to 70.
- Academic, legal, medical writing — grade 12 and above. Flesch Reading Ease below 50. Audience knows the jargon.
What gets flagged
- Long sentences. Anything past 25 words. These are the single biggest readability killer — split them into two or three shorter sentences.
- Passive voice. Detected by a form of to be (am, is, are, was, were, be, been, being) followed by a past participle. Some passives are fine; aim to keep them below roughly ten percent of sentences.
Readability scores are heuristics, not verdicts. Use them as a sanity check after editing — not as a goal in themselves. A score of 60 with the wrong message is still wrong.
Frequently Asked Questions
Which readability score should I trust?
No single score is authoritative — each formula weighs sentence length and word complexity slightly differently. Flesch Reading Ease is the most cited for general copy; Flesch-Kincaid Grade Level is the U.S. school-grade equivalent; Gunning Fog and SMOG were designed for educational and medical writing. Look at all four and check that they roughly agree.
What is a good grade level for consumer copy?
Marketing copy, news websites, and product pages typically aim for grade 6 to 8 — about the reading level of an average adult. Technical documentation can go higher (10 to 12), but anything above grade 14 starts to lose general audiences quickly.
Why is passive voice flagged?
Passive voice constructions (was thrown, is being reviewed) tend to be wordier, weaker, and harder to scan than the active equivalent. They are not wrong, but in editorial copy you usually want to keep them under 10 percent of sentences.
Does the checker work for languages other than English?
No. Flesch and Flesch-Kincaid formulas were calibrated for English syllable patterns and sentence structure. Running them on other languages will produce numbers, but those numbers will not be meaningful.
Is my text stored anywhere?
No. Analysis runs entirely in your browser — nothing is sent to a server. The text is encoded into the URL only so you can bookmark or share a specific analysis.