Text & Writing

Readability Checker

Flesch, Gunning Fog, SMOG and Coleman-Liau with a reading age.

What it does. Readability formulas estimate reading difficulty from sentence length and word length. They are proxies, not comprehension tests — a formula cannot tell whether your writing makes sense. What they measure well is whether your sentences are too long, which is the single most common cause of hard-to-read prose.

Runs in your browserNothing uploadsNo signupWorks offline

How to use Readability Checker

Paste the text.
Read the scores and the estimated reading age.
Look at the flagged sentences — they are the ones raising the grade.

What the numbers mean

What the numbers mean
Flesch Reading Ease	Reads like	Grade
90–100	Very easy — a comic	5th grade
70–89	Easy — popular fiction	6th–7th
60–69	Plain English	8th–9th
50–59	Fairly difficult — broadsheet	10th–12th
30–49	Difficult — academic	College
0–29	Very difficult — legal, technical	Graduate

Aim for 60 or above for general web writing. Most plain-language guidelines, and several government accessibility standards, target roughly the same band — around a 9th-grade level, which is where the median adult reads comfortably rather than at their limit.

What the formulas actually count

Almost all of them use two inputs: average sentence length and average word length or syllable count. That is the whole model.

The consequence is that they can be gamed and misled. Chopping every sentence in half improves the score without improving anything. A short sentence of unfamiliar jargon scores well and communicates nothing.

Flesch Reading Ease — syllables per word and words per sentence. The most cited.
Flesch-Kincaid Grade — the same inputs expressed as a US school grade.
Gunning Fog — weights words of three or more syllables.
SMOG — designed for health materials, and the one most often required in that field.
Coleman-Liau — uses characters rather than syllables, so it is more reliable on text with unusual words.

Where they disagree, the disagreement is informative: a good Flesch with a bad Coleman-Liau usually means short sentences made of long words.

Using the score honestly

Treat it as a smoke alarm rather than a grade. A poor score reliably indicates long sentences; a good score does not indicate good writing.

The productive use is the sentence list rather than the number — find the three worst sentences and rewrite those.

Some things should score badly. A legal clause, a research method or an API reference is precise before it is readable, and simplifying it past the point of accuracy makes it worse. The formula does not know which kind of document it is reading.

Frequently asked questions

What is a good readability score?

For general web writing, Flesch Reading Ease of 60 or above — roughly a 9th-grade level. That is where the median adult reads comfortably rather than at their limit.

Why do the formulas disagree with each other?

They weight different things. Flesch counts syllables, Coleman-Liau counts characters, Gunning Fog weights long words heavily. A good Flesch with a poor Coleman-Liau usually means short sentences made of long words.

Can I just shorten every sentence to improve the score?

You can, and it often will not improve the writing. The formulas measure length, not sense. Use the score to find the worst sentences, then rewrite those for clarity rather than for the metric.

Should technical writing score well?

Not necessarily. A legal clause or an API reference is precise before it is readable, and simplifying past the point of accuracy makes it worse. The formula cannot tell which kind of document it is reading.

Which formula do health materials use?

SMOG, most often. It was designed for exactly that purpose and is frequently the one specified by health-literacy guidelines.