Readability Checker
Six reading scores and the sentences dragging them down — no server.
Everything runs inside your browser. Your files never leave your device.
Input
Result
Ask about Readability Checker
Questions about what this tool does, which option to pick, or what it can and cannot handle.
The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong. The tool itself is not guessing: it runs deterministic code on your device.
About the Readability Checker
This is the one page in the AI category that sends nothing anywhere. Readability scores are arithmetic — every formula here is a fixed sum over four counts of sentences, words, syllables and letters, published between 1948 and 1975 — so they are computed on your own machine, in the tab you are reading this in, and the text you paste never leaves the device. Asking a language model for a Flesch score would be slower, less repeatable, and would have to be believed rather than checked.
Six scores come back at once, and their disagreement is informative rather than a fault. Flesch Reading Ease runs backwards from the others: a hundred is easy, thirty is hard, and sixty to seventy is the plain English most newspapers aim at. Flesch–Kincaid, Gunning Fog, SMOG, Coleman–Liau and the Automated Readability Index all report a school year instead. They differ in what they punish. Coleman–Liau and ARI count letters, so long words hurt regardless of how they are pronounced. Flesch and SMOG count syllables, so polysyllables specifically hurt. A document of short Latinate words scores differently under each, and seeing the spread tells you which problem you have.
Counting is where these tools usually go wrong, so it is done carefully here. Sentence splitting recognises abbreviations, initials, decimals, version numbers and ellipses, because a naive split on full stops turns "Dr. Rao at 4 p.m." into four sentences and every score that depends on words-per-sentence comes out flattering and wrong. Syllable counting is a documented heuristic — it has to be, since English spelling stopped being phonetic centuries ago — and every published formula was calibrated against hand counts, so a shared approximation is the honest thing to use.
The list of your longest sentences is usually more actionable than any of the numbers. Sentence length is the single largest lever in five of the six formulas, and reading your own thirty-eight-word sentence out of context is the fastest way to see it needed splitting.
Run your text through the simplifier and measure it again to see the change as a number.
How to use it
- 1Paste the text. Around a hundred words or more, since these formulas average over sentences and settle down slowly.
- 2Read the Flesch Reading Ease row first — it is the one that reports ease rather than school year.
- 3Look at the spread between the six. A wide gap tells you whether long words or long sentences are the problem.
- 4Set the sentence-length threshold and read the flagged sentences aloud.
- 5Edit, paste it back, and watch the numbers move.
Questions
- Is my text sent anywhere?
- No. This page is the exception in its category: the counting and the arithmetic happen in JavaScript in your own tab, and there is no request to any server at all. Disconnect from the network and it carries on working, which is proof rather than assurance.
- Why do the six scores disagree?
- Because they measure different things. Letter-counting formulas punish long words whatever their rhythm; syllable-counting ones punish polysyllables specifically; Gunning Fog weighs the proportion of three-syllable words heavily. A wide spread across the six is itself a finding, and usually points at a document with either short sentences full of long words or the reverse.
- How accurate is the syllable counting?
- It is a heuristic, and it is described as one deliberately. It counts vowel groups, drops a silent terminal e and knows a few endings that add a beat. It is right for most ordinary English and wrong for loanwords, names and irregular spellings. Every published formula was built on hand-counted syllables, so an approximation is the standard basis.
- Why does SMOG carry a warning on short passages?
- Because SMOG was defined for samples of thirty sentences or more and is noisy below that. Scaling it to a shorter document is what every calculator does, and the note appears so you read that row as an indication rather than a score.
- What score should I aim for?
- Around school year eight, or a Flesch Reading Ease near sixty, for general audiences — that is roughly where most newspapers sit. Technical documentation for specialists can sit higher without being a problem. A public-facing form or a safety instruction should be considerably lower.