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Readability Score Calculator🔒 100% local
Flesch-Kincaid scoring. Privacy-first, no server uploads, no tracking.
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Scores pasted prose with three classic formulas. It splits the text on sentence-ending punctuation, matches words with /[a-z']+/, estimates syllables by counting vowel groups, then computes Flesch Reading Ease with a grade band, the Flesch-Kincaid grade and the Gunning Fog index, along with the word, sentence and syllable counts behind them.
How to use it
- Paste the text you want scored.
- Press Process.
- Read the counts and averages first, then the three scores - Flesch also gets a plain-language band.
Worked example
The quick brown fox jumps over the lazy dog.becomes=== Readability ===
Words: 9
Sentences: 1
Syllables: 11 (estimated)
Avg words/sentence: 9.0
Avg syllables/word: 1.22
Flesch Reading Ease: 94.3 → 5th grade (very easy)
Flesch-Kincaid Grade: 2.3
Gunning Fog Index: 3.6 (years of education needed)
Interpretation:
Flesch 60-80 = plain English, most readable for the web.
FK Grade ~8 = targeting a general audience.
Fog < 12 = accessible to most readers.The cat sat on the mat. The dog ran fast.becomes=== Readability ===
Words: 10
Sentences: 2
Syllables: 10 (estimated)
Avg words/sentence: 5.0
Avg syllables/word: 1.00
Flesch Reading Ease: 117.2 → 5th grade (very easy)
Flesch-Kincaid Grade: -1.8
Gunning Fog Index: 2.0 (years of education needed)
Interpretation:
Flesch 60-80 = plain English, most readable for the web.
FK Grade ~8 = targeting a general audience.
Fog < 12 = accessible to most readers.Two very short sentences score 117.2 on Flesch. The scale is not capped at 100, and the band function still reports '5th grade (very easy)'.
When to use it
- Checking a help page, error message or onboarding email against a target reading grade before publishing.
- Comparing two versions of the same paragraph to see which one is easier to read.
- Producing a Flesch-Kincaid figure for documentation or a paper that has to cite one.
What it does not do
- Sentences are split on runs of . ! or ? followed by whitespace, so abbreviations and decimals inflate the count: 'Dr. Smith paid 3.50 dollars. He left.' is reported as 3 sentences and 6 words, and every score moves with it.
- Syllables come from a vowel-group regex with a few suffix rules, not a dictionary, so the estimate drifts on unusual words and names. Flesch-Kincaid is the most sensitive of the three to that error.
- Words are matched with /[a-z']+/, which discards digits and every non-ASCII letter: accented words lose characters silently, and a non-Latin sample throws 'No words found.'.
- Short samples are not meaningful. Sentence count is forced to at least 1, so a single ten-word sentence reads as 117.2 on Flesch with a negative Flesch-Kincaid grade.
- There is no per-sentence or per-paragraph breakdown, so one unreadable paragraph inside otherwise easy text is reported only as a blended average.