Six formulas, not one
They disagree constantly, and the disagreement is the useful part: Gunning Fog points at your long words, Coleman-Liau never guesses a pronunciation, SMOG counts polysyllables and nothing else.
Readability Analyzer
Six readability formulas at once, with the hard sentences marked where they sit.
- Input
- No upload needed — instant
- Privacy
- Nothing is uploaded
- Cost
- Free · no sign-up · no watermark
Loading tool…
The tool is loading its code on your device. This happens once and is cached for later visits.
Processed entirely on your device
Everything you type or paste is handled by JavaScript running in this tab. No request is sent, nothing is logged and nothing is stored. Close the page and it is gone.
Overview
About the Readability Analyzer
Measure how easy your text is to read with Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau and ARI — plus an inline overlay that marks every hard sentence, passive verb and long word.
A readability score is not an opinion about your writing. It is arithmetic over four counts — words, sentences, syllables and letters — fitted to real readers between the 1940s and the 1970s. That is why it is useful and why it is limited in the same breath: it measures the surface of a sentence reliably, and it measures nothing else at all.
A legal contract scores terribly. A children's book scores beautifully. Neither result is wrong, and neither says anything about whether the document does its job. What the numbers are genuinely good for is comparison — this draft against last week's, this paragraph against the one an editor bounced, this page against the reading level your audience actually has.
The six formulas
All six are shown here, each on its own scale, because they disagree constantly and the disagreement is information rather than noise.
Two of them need a syllable count, which means a pronunciation guess. English spelling is not a phonetic system, so any syllable counter is a heuristic: it handles ordinary prose well and stumbles on names and on words whose spelling has drifted from their sound. Coleman-Liau was invented specifically to avoid that problem by counting letters instead, and ARI goes further and counts characters. That difference is the main reason the six disagree, and it is a design choice rather than an error in any of them.
Gunning Fog is the harshest of the group on long words: it adds the percentage of three-syllable-plus words straight into the sentence average, so a paragraph of technical nouns pushes it up hard even when every sentence in it is short. SMOG counts polysyllables and nothing else, and was built for patient-leaflet writing, where it remains the standard. On technical text, expect both to read high and take that as a signal about your nouns rather than about your sentences.
What the bands mean
Reading Ease runs from 0 to 100. Above 90 is very easy, 80 to 90 easy, 70 to 80 fairly easy, 60 to 70 standard plain English, 50 to 60 fairly hard, 30 to 50 difficult, and below 30 very difficult. Most general-audience web copy aims for the 60 to 70 band.
The five grade levels are reported as years of schooling: up to 5 is roughly age 10 or 11, up to 8 age 13 or 14, up to 12 high school, up to 16 college, and past that post-graduate.
Every band on this page is the engine's own, which is why the colour of a row and the words inside it can never contradict each other. Inventing a second set of thresholds in the interface is the easiest way to build a page that looks like it disagrees with itself.
Where the difficulty actually sits
A number at the top of a page does not tell anybody which sentence to open, and fixing readability is sentence-level work. That is what the second half of this tool is for.
Every sentence is scored on its own and marked hard or very hard. A sentence is very hard below Reading Ease 30, or below 50 once it reaches 25 words; it is hard below 50, or over 20 words. Those are the measurement's own thresholds, not a second opinion layered on top of them.
The overlay paints two layers at once without them fighting. Sentence difficulty is a background — red for very hard, amber for hard. Word-level marks are underlines: wavy for passive voice, solid for words of three or more syllables, dotted for adverbs. Two shapes of marking rather than five colours, so both layers stay legible on the same text and remain distinguishable if you do not see colour the way most people do.
Adverbs start switched off. They are the noisiest of the five by a wide margin — every -ly word of five letters or more, plus the common intensifiers that carry no -ly at all — and on an ordinary article that is a pageful of dotted lines drowning the two highlights that carry a verdict. Switch them on for marketing copy, where the count really is worth seeing.
The rhythm strip shows sentence lengths in document order, deliberately unsorted. The point is to see whether the difficulty is spread evenly through the piece or piled into one paragraph, and sorting would destroy exactly that. A strip of even-height bars is the visual signature of machine-written prose, whatever the words in it say, which is why the AI Content Detector charges for the same pattern.
When not to trust the numbers
Below about 30 words or three sentences the figures are still calculated, still correct, and still close to meaningless. All six formulas are averages, and an average over two sentences swings by ten grade levels on a single long word: paste a heading and you will be told it reads at post-graduate level. The page says so rather than hiding the result, because refusing to answer is worse than answering with the caveat attached.
Two further limits are worth carrying into any decision you make with these figures. Syllable counting is a heuristic, so scores on text dense with names or technical vocabulary carry a margin of about a grade. And all six measure surface rather than sense: a paragraph can score beautifully and say nothing at all, while the clearest sentence in the world can still be the wrong one to write.
Use the numbers to compare two drafts of the same thing, and use the marked text to decide which sentence to open. Everything is calculated in this tab as you type — nothing is uploaded and nothing is stored, which makes it safe for unpublished work. If you want the marks acted on rather than just shown, the AI Text Humanizer runs the same analysis and rewrites what it finds.
Step by step
How to use the Readability Analyzer
Paste the article, page copy, essay or email you want measured — every figure updates as you type.
Read the headline Flesch Reading Ease score and its band, then compare all six formulas in the table underneath.
Check the sentence rhythm strip to see whether the difficulty is spread through the piece or piled into one paragraph.
Read your text marked: hard sentences shaded, passive voice, long words and adverbs underlined, each switchable.
Open the hardest-sentences list and rewrite those first, then copy the full report.
Why use it
Benefits and common use cases
What this tool is good for, and what it deliberately does not try to do.
Marked where the problem sits
A score does not tell you which sentence to open. Every hard sentence, passive verb, long word and adverb is highlighted in place, using the offsets the measurement itself produced.
Bands come from the measurement
Every label and every colour is the engine's own verdict band rather than a second opinion layered on top, so a row can never read "high school" in green beside one reading the same words in amber.
Live, and entirely private
Calculated on your own device as you type, on a deferred value so a long paste never makes the textarea lag. Nothing is uploaded and nothing is stored.
Questions
Frequently asked questions
Short, honest answers about quality, limits and privacy.
Which readability formula should I use?
For general web copy, Flesch Reading Ease — it is the most widely recognised and the only one of the six published on a 0-100 scale. For anything aimed at patients or the public under a compliance requirement, SMOG, which is still the standard for health leaflets. For technical writing, look at Gunning Fog, because it is the one that will tell you honestly how many long nouns you are using.
What is a good Flesch Reading Ease score?
60-70 is plain English and the target most general-audience pages aim for. Above 80 reads as easy, above 90 as very easy — roughly a children's book. Below 50 is fairly hard, below 30 difficult, and below that the text is being read by specialists or by nobody.
Why do the six formulas disagree?
Because they measure different things and were fitted on different corpora in different decades. Two of them need a syllable count, which means a pronunciation guess. Coleman-Liau counts letters instead, specifically to avoid that guess, and ARI counts characters. Gunning Fog weights long words far more heavily than the others. A spread of two or three grade levels across the six is normal.
How are syllables counted?
By a vowel-group heuristic: consecutive vowels count once, a silent trailing e is dropped, and a few endings are handled as special cases. It is accurate on ordinary English prose and approximate on names, technical terms and words whose spelling has drifted from their pronunciation, which is why scores on heavily technical text carry a margin of about a grade.
Why does a short paste score so badly?
All six formulas are averages, and an average over two or three sentences moves by ten grade levels on one long word. Paste a single heading and you will be told it reads at post-graduate level, which is arithmetically true and practically meaningless. The page flags anything under 30 words or three sentences rather than letting a confident-looking number stand on its own.
Does a high grade level mean the writing is bad?
No. A legal contract scores terribly and a children's book scores beautifully, and neither result is a judgment about quality. The formulas measure surface features — syllables, sentence length, word length — and are blind to sense. Use them to compare two drafts of the same thing against the reading level your audience actually has, not to grade the writing.