lexicon.consonant-cluster

What it flags

Words whose longest run of consecutive consonants meets or exceeds a per-profile threshold. Dense consonant clusters are a known decoding barrier for dyslexic readers (BDA Dyslexia Style Guide): the reader must hold more phonemes in working memory before the next vowel “releases” the syllable.

Typical English offenders at the public threshold of 5 include strengths (n-g-t-h-s), twelfths (l-f-t-h-s), sixths (x-t-h-s in a 4-run plus context). Typical French offenders at the falc threshold of 4 include constructions (n-s-t-r).

At a glance

Detection

Per source line, walk the grapheme stream once. A word is a maximal run of alphabetic characters; hyphens, apostrophes, and whitespace close the word (so dys-lexic is two words, not one ten-letter cluster). Within a word, track the longest run of consecutive consonants. Emit one diagnostic per word whose longest run meets min_run_length.

Vowels are language-aware — French accented forms (é, è, ê, à, â, î, ï, ô, ö, ù, û, ü, ÿ, œ, æ) count as vowels. The English fallback still accepts common latin-1 accented vowels so borrowed words (café, naïve) decode correctly. y is treated as a vowel in every language (lenient), which avoids awkward false positives on words like fly, rhythm.

Parameters

dev-doc is tolerant — technical prose regularly names things like strengths and benchmarks. falc (plain-language audience) catches any 4-consonant run.

Known caveats

• The rule is blind to syllable structure: it counts raw consonant graphemes, not phonemes. A word like hatching (5 letters: t-c-h-n-g — a run of 5) reads fluently to most readers because tch is a single English digraph. Suppress with an inline directive when a hit is unavoidable.
• Script-agnostic for any alphabetic script, but the vowel lists are tuned for Latin scripts only. Words in Cyrillic, Greek, Arabic, etc., will likely trigger whenever the language flag is en or fr — in practice such content is out of scope for a bilingual EN/FR linter.

Suppression

See Suppressing diagnostics.

See also

• lexicon.all-caps-shouting
• readability.score
• Conditions

References

• Seidenberg et al. (1984)
• Treiman et al. (2006)

See References for the full bibliography.