Readability Checker
Analyse text readability with six formulas: Flesch Reading Ease, Flesch-Kincaid Grade, Gunning Fog, Coleman-Liau, SMOG, and ARI. Flags long sentences and shows detailed stats.
The Readability Checker is a free, browser-based tool that analyses how easy a piece of text is to read. It computes six widely used readability scores, identifies long sentences, and shows detailed text statistics. All processing runs entirely in your browser — no text is uploaded.
Features
| Feature | Detail |
|---|---|
| Six readability scores | Flesch Reading Ease, Flesch-Kincaid Grade, Gunning Fog, Coleman-Liau, SMOG, and ARI |
| Visual gauge | Colour-coded Flesch Reading Ease bar from Very Hard to Very Easy |
| Long sentence detection | Lists all sentences over 25 words with word counts |
| Text statistics | Word count, sentence count, total syllables, average words per sentence, average syllables per word, complex word percentage |
| Strip HTML | Automatically removes HTML tags before analysis |
| File support | Load .txt, .md, or .html files directly |
How to Use
- Paste your text into the input area, or click Load file to upload a file.
- If your text contains HTML markup, enable Strip HTML tags.
- Click Analyse.
- Review the statistics bar, the six score cards, the readability gauge, and the long sentences list.
Readability Scores
Flesch Reading Ease
The Flesch Reading Ease formula (1948) produces a score between 0 and 100. Higher scores mean easier reading. It uses average sentence length and average syllables per word.
| Score | Difficulty | Typical audience |
|---|---|---|
| 90-100 | Very Easy | 5th grade |
| 80-90 | Easy | 6th grade |
| 70-80 | Fairly Easy | 7th grade |
| 60-70 | Standard | 8th-9th grade |
| 50-60 | Fairly Difficult | 10th-12th grade |
| 30-50 | Difficult | College |
| 0-30 | Very Confusing | College graduate |
Flesch-Kincaid Grade Level
A US school grade equivalent derived from the same inputs as the Flesch Reading Ease score. A score of 8 means the text can be understood by an average 8th grader. This formula is used by US government agencies, including the Department of Defense, as a standard for document readability.
Gunning Fog Index
The Gunning Fog formula (1952) estimates the years of formal education a reader needs to understand the text on a first reading. It weights the percentage of complex words (three or more syllables) heavily. A score of 12 corresponds to 12th grade; most popular newspapers target a Fog index of 10 to 12.
Coleman-Liau Index
Unlike most readability formulas, Coleman-Liau uses the average number of characters per word rather than syllables. This makes it easier to compute and well-suited for analysing text where syllable counting may be ambiguous. It also outputs a US grade level equivalent.
SMOG Index
SMOG (Simple Measure of Gobbledygook) counts three-syllable-or-more words and uses the square root of their frequency to estimate grade level. It is particularly popular in health communication research. Note: SMOG is most accurate with 30 or more sentences; the tool flags this with a warning on shorter text.
Automated Readability Index (ARI)
ARI uses characters per word and words per sentence to estimate grade level. It is one of the few formulas that does not rely on syllable counting, making it fully deterministic and fast to compute for large documents.
Understanding the Scores
No single formula is definitively correct — each weights different factors and was validated on different corpora. For most general writing purposes, aim for:
- Flesch Reading Ease above 60 for general audience web content
- Grade level below 9 for consumer-facing writing
- Gunning Fog below 12 for business and journalism
- Average sentence length below 20 words as a practical target
Use the long sentences list to identify candidates for splitting. Long sentences are the quickest win for improving readability scores.
Frequently Asked Questions
Which readability score should I focus on?
Flesch Reading Ease is the most widely cited and understood. Pair it with the Flesch-Kincaid Grade Level for a grade-equivalent reference. Use Gunning Fog if complex vocabulary is a particular concern.
Why do the scores differ from each other?
Each formula was developed independently, validated on different text samples, and weights different features. They are correlated but not identical. It is normal for a text to score somewhat differently on each formula.
Does a higher Flesch score always mean better writing?
Not necessarily. Very technical content legitimately requires specialist vocabulary and longer sentences. The appropriate readability level depends on your audience. Medical literature for physicians can reasonably score in the 20-40 range, while a consumer health leaflet should target 60+.
Why is SMOG marked with a note on short texts?
The SMOG formula was designed to be applied to a sample of 30 sentences. With fewer sentences, the formula's statistical basis is weaker. Treat SMOG scores on short texts as rough estimates.
How are syllables counted?
The tool uses a heuristic algorithm for English text: it counts groups of vowels (a, e, i, o, u, y), removes silent trailing e patterns, and ensures every word has at least one syllable. This is accurate for most common English words but may over- or under-count irregular words.
Can I use this for non-English text?
The readability formulas and the syllable counting algorithm are calibrated for English. Using them on other languages will produce numbers, but those numbers will not correspond to the intended reading level scales. For non-English readability analysis, use language-specific tools.
What counts as a complex word?
A complex word is one with three or more syllables. Common suffixes like -ing, -ed, and -es are excluded from the syllable count to avoid inflating scores for ordinary words.
What is a good average sentence length?
Research on plain English writing generally recommends keeping average sentence length between 15 and 20 words. Sentences over 25 words significantly increase cognitive load. The tool flags all sentences over 25 words so you can review and split them.