Formula to detect the grade level of text according to the (revised) Dale–Chall readability formula.

• What is this?
• When should I use this?
• Install
• Use
• API
  • daleChallFormula(counts)
  • daleChallGradeLevel(score)
• Types
• Compatibility
• Related
• Contribute
• Security
• License

This package exposes an algorithm to detect ease of reading of English texts.

You’re probably dealing with natural language, and know you need this, if you’re here!

See dale-chall for a list of words which count as “familiar”. All other words are considered “difficult” for this algorithm.

This package is ESM only. In Node.js (version 14.14+, 16.0+), install with npm:

npm install dale-chall-formula

In Deno with esm.sh:

import {daleChallFormula, daleChallGradeLevel} from 'https://esm.sh/dale-chall-formula@2'

In browsers with esm.sh:

<script type="module">
  import {daleChallFormula, daleChallGradeLevel} from 'https://esm.sh/dale-chall-formula@2?bundle'
</script>

import {daleChallFormula, daleChallGradeLevel} from 'dale-chall-formula'

daleChallFormula({word: 30, sentence: 2, difficultWord: 6}) // => 4.41208

daleChallGradeLevel(daleChallFormula({word: 30, sentence: 2, difficultWord: 6})) // => [9, 10]

This package exports the identifiers daleChallFormula, daleChallGradeLevel. There is no default export.

Given the number of words (word), the number of sentences (sentence), and the number of unique unfamiliar words in a document (difficultWord), returns the score associated with the document.

Counts from input document.

Number of sentences (number, required).

Number of words (number, required).

Number of unique unfamiliar words (number, default: 0).

Score representing ease of reading (number).

Pass it to daleChallGradeLevel to get grade levels.

Turn a dale–chall score into U.S. grade levels.

Score representing ease of reading.

Grade levels ([number, number]).

This package is fully typed with TypeScript. It exports the additional type Counts.

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 14.14+ and 16.0+. It also works in Deno and modern browsers.

• automated-readability — uses character count instead of error-prone syllable parser
• coleman-liau — uses letter count instead of an error-prone syllable parser
• flesch — uses syllable count
• flesch-kincaid — like flesch-formula, returns U.S. grade levels
• gunning-fog — uses syllable count, needs POS-tagging and NER
• smog-formula — like gunning-fog-index, without needing advanced NLP
• spache-formula — uses a dictionary, suited for lower reading levels

Yes please! See How to Contribute to Open Source.

This package is safe.

MIT © Titus Wormer