Measure vocabulary sophistication: average word length, rare word percentage, CEFR vocabulary estimate, and ratio of common-to-advanced words. Highlights advanced vocabulary and surfaces jargon density.
Built and maintained by Paul Clark, Redmoon Software
Use when writing for non-native readers, simplifying technical docs, or checking that marketing copy isn't accidentally academic.
Pairs with Dale-Chall (which scores familiarity directly) and lexical density (information packing). All three together describe vocabulary load comprehensively.
Every word is bucketed as "everyday" (in the combined Dale-Chall + stopword list) or "advanced" (everything else).
CEFR estimate is derived from the advanced-word percentage: < 10% A1, < 20% A2, < 30% B1, < 45% B2, < 60% C1, else C2.
Jargon density is the percent of words ≥ 8 characters, a rough proxy for technical Latin/Greek-rooted vocabulary.
CEFR levels (A1, A2, B1, B2, C1, C2) describe reader vocabulary thresholds for non-native English learners. Higher = more advanced vocabulary load.
We use a combined list of English stopwords and the Dale-Chall 3,000 most familiar words. Anything outside is treated as advanced.
Not always. Audience-appropriate vocabulary beats clever-sounding vocabulary every time.
Input
The municipal infrastructure necessitates comprehensive remediation prior to subsequent occupancy.
Output
78% advanced — CEFR ~C2.
Seven of nine words fall outside the everyday vocabulary list, including Latin-rooted terms ("municipal", "necessitates", "remediation"). Average word length is over 9 characters.
Sophistication is estimated by where a text's words sit in general English usage frequency. Words from the common core are unmarked; words from the long tail of rarer vocabulary are what make text feel advanced. This is a better proxy than word length, because plenty of long words are entirely ordinary and plenty of short ones are not.
It measures reader burden, not writer skill. A high figure means an audience needs a broad vocabulary to read comfortably. Whether that is appropriate is a decision about who the audience is.
For most practical writing a rising sophistication score is a warning rather than an achievement. Rarer vocabulary is slower to process even for readers who know every word, and the gain in precision is usually smaller than writers assume — most "elevated" word choices are near-synonyms of the plain word rather than genuinely more exact.
The exception is genuine terminology. A technical term that names a concept precisely earns its place however rare it is, and replacing it with a common approximation makes the text worse. The distinction is whether a rare word is doing work no common word could.
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