Readability CheckerFlesch-Kincaid, Gunning Fog and More

A page can be accurate and still lose readers if every sentence runs on for forty words. Kwebby's Readability Checker puts a number on that problem. Paste your text and it scores how hard the writing is to read with 10 established formulas, including Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog, SMOG and Coleman-Liau. An optional AI report adds a per-formula breakdown and suggestions. It is free, and you do not need an account.

Key Takeaways

• Kwebby's Readability Checker scores pasted text with 10 readability formulas as you type, in your browser. An optional AI report adds improvement suggestions. It needs no account.
• Flesch Reading Ease runs from 0 to 100, and higher means easier. The standard table puts 60 to 70 at "plain English" for 8th and 9th graders.
• Gunning Fog estimates the years of education needed to read a text. A score under 12 suits a wide audience, and under 8 suits near-universal understanding.
• Hemingway Editor recommends an 8th-grade level as a baseline, because it describes that as the average adult reading level in the United States.
• Formulas measure sentence length and word length. They cannot judge accuracy, tone or whether your advice is any good.
• Flesch Reading Ease and Flesch-Kincaid Grade Level cannot be converted into each other, so compare scores from the same formula.

What Is the Kwebby Readability Checker?

The Kwebby Readability Checker is a free web tool that measures how easy a piece of text is to read. You paste your writing into the box, and the scores appear as you type, with no button to press. The tool runs 10 readability formulas in your browser, and a Generate AI Report button adds a per-formula breakdown with improvement suggestions.

A readability score is an estimate based on the shape of your text, mostly how long the sentences are and how long the words are. It tells you where writing is likely to feel heavy. It does not replace a reader's opinion, but it is a quick, consistent way to find the sentences worth fixing.

Key Features and How It Works

The tool is built around one input and a set of scores. These are the parts you will use.

Paste Your Text

Scores appear once the box holds at least one sentence and five words. They update as you type. A longer sample gives steadier numbers than a single sentence, so paste a full section or article when you can. The scores are calculated in your browser, so the text is not sent anywhere unless you ask for the AI report.

Scores From Multiple Formulas

The tool runs 10 formulas: Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index, SMOG Index, Coleman-Liau Index, Automated Readability Index (ARI), Linsear Write, Lix, Rix and Powers-Sumner-Kearl. It also shows a consensus grade, which is the average of the seven grade-level formulas. Running several formulas gives you a range instead of a single opinion.

Next to the scores, the tool lists text statistics: words, sentences, paragraphs, syllables, average sentence length, complex words (three or more syllables), long sentences (over 20 words), reading time at 238 words per minute and speaking time at 125 words per minute.

The formulas count English syllables, so the tool scores English text only. If you paste text in another script, such as Cyrillic or Chinese, it tells you it cannot score it. Very long texts are scored on the first 100,000 characters.

An AI Report With Suggestions

Click Generate AI Report to get a written report. The tool sends the scores, the statistics and the first 300 characters of your text to Kwebby's server, which asks an AI language model through OpenRouter for a per-formula breakdown, the main issues, your strengths and improvement suggestions. The report is optional, and the scores work without it.

Share and Report

Share buttons let you pass the page on, and a "Report if not working" link lets you flag a problem.

Readability Formulas Explained

Each formula looks at slightly different features of your text. Knowing what they measure helps you read the numbers.

Flesch Reading Ease

Flesch Reading Ease scores text from 0 to 100, and higher scores are easier. In the standard table on the Flesch-Kincaid tests page, 80 to 90 is "easy to read" and suits 6th grade, 70 to 80 is "fairly easy" at 7th grade, and 60 to 70 is "plain English" at 8th and 9th grade. Scores of 50 to 60 are "fairly difficult" at 10th to 12th grade, and 30 to 50 are "difficult" at college level.

Flesch-Kincaid Grade Level

This formula uses the same core measures, word length and sentence length, with different weighting. It presents the result as a US school grade level, so a score of 8 means roughly the 8th grade. The two Flesch scores are not directly comparable and cannot be converted into one another.

Gunning Fog Index

The Gunning Fog Index adds the average sentence length to the percentage of complex words, those with three or more syllables, and multiplies the sum by 0.4. The Gunning fog index article says texts for a wide audience generally need an index under 12, and texts that need near-universal understanding generally need one under 8.

SMOG Index

SMOG stands for Simple Measure of Gobbledygook. It counts words with three or more syllables across samples of sentences. The SMOG article notes it is widely used for checking health messages, and that its tables are statistically invalid for texts under 30 sentences. Treat SMOG on a short paragraph with caution.

Coleman-Liau Index

Coleman-Liau uses letters per 100 words and sentences per 100 words, with no syllable counting. That makes it easier for software to compute reliably. Like the others, it outputs an estimated grade level.

Why Readability Matters

Readers do not stay to decode long, tangled writing. Clear text gets understood faster, is easier to skim on a phone and serves readers with different backgrounds, including those reading in a second language.

Be careful with the SEO claims you may see elsewhere. No readability score is a confirmed ranking factor, and a better Flesch number will not lift a thin page. The real benefit is indirect: writing that people understand and finish is more likely to be shared, cited and acted on. Use the score as a quality check, not a target to game.

How to Use the Readability Checker

Scoring a text takes five steps.

1. Paste your text. Add at least one sentence of five or more words. For stable scores, paste a full section or article.
2. Read the scores. Note the Flesch Reading Ease, the grade-level formulas and the Gunning Fog value.
3. Generate the AI report if you want one. Click Generate AI Report, then read the per-formula breakdown and the improvement suggestions.
4. Fix the hardest sentences. Split long ones, swap complex words and switch passive voice to active.
5. Paste the revised text and compare. Check that the scores moved in the right direction and the meaning stayed the same.

How to Improve Readability

Most low scores come from the same few habits. Fix these first.

• Shorten sentences. Many style guides suggest an average of 15 to 20 words. The checker counts every sentence over 20 words as long, so split complex sentences into two.
• Use simpler words. Write "use" instead of "make use of" and "start" instead of "commence".
• Prefer active voice. "The dog bit the man" is clearer and shorter than "The man was bitten by the dog".
• Cut filler. Delete words that add no meaning, such as "in order to" where "to" works.
• Break up paragraphs. Short paragraphs of two to four sentences are easier to scan.
• Read it aloud. If you run out of breath, the sentence is too long.

Best Practices for Using Readability Scores

Scores are most useful when you apply them with judgment.

Match the Score to Your Audience

A consumer blog can aim for a plain, conversational level. A technical guide for engineers can score higher without being bad writing. Hemingway Editor's readability guidance uses an 8th-grade baseline for general audiences, and you can adjust from there.

Compare Like With Like

Always compare scores from the same formula, and test the same type of text. A Flesch number from one tool and a Fog number from another say different things.

Do Not Write for the Score

Chopping every sentence to five words raises the score and makes the text choppy. Vary your sentence length, and stop when the text reads naturally.

Keep Technical Terms

Some words are necessary even if they count as complex. Define them once and keep using them.

Use Enough Text

Short samples give noisy results. Paste a full section, not a single sentence, before drawing conclusions.

Fix Grammar First

Errors confuse every formula. Run the text through the Grammar Checker before you score it.

Common Use Cases

• Blog posts and landing pages. Find the heaviest paragraphs before you publish.
• Help and documentation. Keep instructions clear for non-expert readers.
• Health and public information. Check that consumer-facing material is easy to read.
• Student writing. See how a draft's reading level compares with the assignment.
• Rewritten text. Score output from the AI Article Rewriter Pro after using Simplify mode.
• Content audits. Compare reading levels across pages of one site.

Related Kwebby Tools

The Readability Checker belongs to our Text Tools collection. These tools finish the editing pass:

• Grammar Checker fixes grammar, spelling, punctuation and style issues.
• Word Counter Pro counts words, characters and reading time.
• Keyword Density Checker shows how often keywords appear in your content.
• AI Article Rewriter Pro rewrites or simplifies text with AI.
• Plagiarism Checker tests whether your wording matches other pages.

Final Thoughts

A readability score will not write your article, but it will show you where readers are likely to stumble. Paste a draft into the Readability Checker, fix the longest sentences and the heaviest words first, and score it again. Keep the meaning, and aim for natural writing, not a perfect number. Run a grammar pass with the Grammar Checker first, and use the Word Counter Pro to keep your length in check.