Readability Checker: Flesch, Gunning Fog and SMOG
Readability scores plus highlights for long sentences and passive voice.
Use via API
Readability scores for English text (Flesch reading ease, Flesch–Kincaid grade, Gunning fog, SMOG, Coleman–Liau, ARI) plus counts of long sentences, passive voice, adverbs and complex words. Send JSON, get JSON back.
POST https://pithlab.com/api/v1/tools/readability-checker
curl https://pithlab.com/api/v1/tools/readability-checker \
-H "Authorization: Bearer $PITHLAB_KEY" \
-H "Content-Type: application/json" \
-d '{"input":"The cat sat on the mat. It was a sunny day, and the birds were singing loudly in the tall trees."}'About the Readability Checker
Score your writing with Flesch Reading Ease, Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau and ARI, and highlight long sentences, passive voice and adverbs.
How to use the Readability Checker
- Paste your text, ideally a few paragraphs or more.
- Read the six scores. Grade levels are US school grades, and a Flesch Reading Ease of 60 or more is plain English.
- Look at the highlighted text: long sentences, possible passive voice, adverbs and complex words are marked.
- Edit your text elsewhere and paste it again to compare scores.
Examples
Input
The cat sat on the mat. The dog ran.
Output
Flesch Reading Ease 117.7 (Very easy), Flesch-Kincaid Grade -2.0, 2 sentences, 9 words
Input
Readability formulas estimate difficulty. Shorter sentences help.
Output
Flesch Reading Ease -50.5 (Very difficult), Flesch-Kincaid Grade 21.2, 2 sentences, 7 words
Frequently asked questions
How are the scores calculated?
With the published formulas. Flesch Reading Ease is 206.835 minus 1.015 times words per sentence minus 84.6 times syllables per word. Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau and ARI give a US school grade from sentence length plus syllables, complex words or letters per word.
How are syllables counted?
By a rule-based estimate: count groups of vowels (a, e, i, o, u, y) after dropping a silent final e, a silent -ed or -es, and a leading y. Short words count as one syllable. It is right for most English words but not all, which is true of every readability tool, so scores can differ slightly between tools.
How reliable is the passive voice check?
It is a hint, not grammar analysis. It flags a form of "to be" followed by a word ending in -ed or a common irregular participle such as "written", like "was written". Adjectives such as "is tired" can be flagged too, and some passives are missed.
Why does a short text get odd scores?
The formulas were designed for samples of at least 100 words, and SMOG for 30 sentences. With a sentence or two, one long word can swing the score, and Flesch Reading Ease can go below 0 or above 100. Line breaks also end sentences here, so headings and list items count as sentences.
Is my text sent anywhere?
No. All the analysis runs in your browser, so your writing never leaves your device.