Readability Checker

What is a useful readability score for SEO content?

Use this Readability Checker to compare your draft with the reading level you intend to serve. It reports text difficulty, not an SEO grade or a predicted search position. For a general-audience draft, the tool's Standard band is a useful starting point to inspect: Flesch Reading Ease from 60 up to, but not including, 70. This is an interpretation label, not an SEO requirement.

Keep Flesch Reading Ease separate from Flesch-Kincaid Grade. A higher Ease score means simpler text, while a lower grade estimate means a lower estimated school reading level. A score of 65 on the first scale is not Grade 65 on the second. The interface labels Ease as a score out of 100 and the other formula results as grades.

How does splitting a sentence change the scores?

Paste this deliberately repetitive example: The cat sat on the mat and the dog ran home fast; the cat sat on the mat and the dog ran home fast. The checker counts 24 words, one sentence, and 24 estimated syllables. Replace the semicolon with a period and capitalize the next word. The vocabulary stays the same, but the sentence count becomes two.

The Flesch Reading Ease formula gives 206.835 − 1.015 × 24 − 84.6 × 1 = 97.875 before the split, displayed as 97.9. Afterward its raw result is 110.055, but this implementation caps Ease at 100. Flesch-Kincaid Grade changes from 0.39 × 24 + 11.8 × 1 − 15.59 = 5.57 to 0.89. The example also shows a limitation: formulas reward shorter sentences without judging repetition or whether the writing is useful.

How are the six readability formulas calculated?

Let W mean word count, S sentence count, Y estimated syllables, C complex word occurrences, and A ASCII letters plus digits. The checker uses the following calculations and displays scores rounded to one decimal place. Grade estimates are floored at zero.

• Flesch Reading Ease: 206.835 − 1.015 × (W ÷ S) − 84.6 × (Y ÷ W), limited to 0–100.
• Flesch-Kincaid Grade Level: 0.39 × (W ÷ S) + 11.8 × (Y ÷ W) − 15.59.
• Gunning Fog Index: 0.4 × ((W ÷ S) + 100 × C ÷ W). Here every occurrence with at least three estimated syllables counts; there is no proper-name exclusion.
• Coleman-Liau Index: 0.0588 × (100 × A ÷ W) − 0.296 × (100 × S ÷ W) − 15.8. This implementation's character count includes digits.
• Automated Readability Index: 4.71 × (A ÷ W) + 0.5 × (W ÷ S) − 21.43.
• SMOG Index: the implemented calculation is 3 + √(C × 30 ÷ S). It appears from three sentences, with a directional warning below 30 sentences.

Overall Readability appears only at 30 words or more. It interprets the average of the displayed Flesch-Kincaid, Gunning Fog, and Coleman-Liau values. It excludes Ease, SMOG, and Automated Readability. A difference between that summary and one individual row therefore does not mean the calculations failed.

How can highlights and complex words guide an edit?

Click Highlight: Off to replace the visible editor with sentence shading. Sentences of 15 words or fewer remain unshaded; 16–25 words use light amber, 26–35 use stronger amber, and 36 or more use red. Click Highlight: On to return to editing. Split a sentence where it contains two separate ideas, then compare the updated scores.

Complex Words counts occurrences with at least three estimated syllables. The expandable list instead shows unique lowercase words in alphabetical order, so a repeated term can increase the statistic several times while appearing once in the list. Keep necessary terminology and explain it when needed. The checker does not replace words or rewrite sentences for you.

Passive Voice is a separate heuristic, not an input to the six formulas. It detects a listed form of “be” immediately followed by a word ending in “ed.” For example, The file was saved. The team wrote it. We sent it. gives 33% because one of three sentences matches. It misses irregular participles such as “written,” so 0% does not prove that every sentence is active.

What text should you enter for a meaningful check?

Paste the English passage your readers will actually see, with sentence-ending punctuation. The engine counts whitespace-separated tokens as words and uses periods, question marks, and exclamation marks to identify sentences. A semicolon does not create a new sentence. If some sentences have terminal punctuation but the final fragment does not, that fragment is not counted as an additional sentence even though its words remain in the word count.

Syllables are estimated using English vowel groups and ending rules rather than a pronunciation dictionary. Names, abbreviations, and non-English passages need manual judgment. Blank lines separate paragraphs. A single line break does not necessarily create a new paragraph. Avoid comparing a complete article with an isolated headline as though they were equivalent samples.

The tool analyzes pasted text or a local .txt file read as UTF-8; it does not fetch a website URL or extract text from a PDF. Its calculation runs in the browser on the supplied text. Use the Word Counter for a broader text overview and the Keyword Density Checker to inspect repeated terms. These answer different editing questions within the SEO tools collection.