Project: retextjs/retext-readability

Package: retext-readability@7.2.0

  1. Dependents: 0
  2. retext plugin to check readability
  1. unified 179
  2. plugin 137
  3. retext 42
  4. retext-plugin 26
  5. reading 3
  6. readability 2


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retext plugin to check readability.


What is this?

This package is a unified (retext) plugin to check readability: whether your presumed target audience can read your prose. It applies Dale—Chall, Automated Readability, Coleman-Liau, Flesch, Gunning-Fog, SMOG, and Spache.

When should I use this?

You can opt-into this plugin when you’re dealing with content that might be difficult to read to some folks, and have authors that can fix that content.

💡 Tip: I also made an online, editable, demo, similar to this project: wooorm.com/readability.


This package is ESM only. In Node.js (version 12.20+, 14.14+, 16.0+, or 18.0+), install with npm:

npm install retext-readability

In Deno with esm.sh:

import retextReadability from 'https://esm.sh/retext-readability@7'

In browsers with esm.sh:

<script type="module">
  import retextReadability from 'https://esm.sh/retext-readability@7?bundle'


Say our document example.txt contains:

The cat sat on the mat

The constellation also contains an isolated neutron
star—Calvera—and H1504+65, the hottest white dwarf yet
discovered, with a surface temperature of 200,000 kelvin

…and our module example.js looks as follows:

import {read} from 'to-vfile'
import {reporter} from 'vfile-reporter'
import {unified} from 'unified'
import retextEnglish from 'retext-english'
import retextStringify from 'retext-stringify'
import retextReadability from 'retext-readability'

const file = await unified()
  .process(await read('example.txt'))


…now running node example.js yields:

  3:1-5:57  warning  Hard to read sentence (confidence: 4/7)  retext-readability  retext-readability

⚠ 1 warning

The target age is 16 by default, which you can change. For example, to 6:

-  .use(retextReadability)
+  .use(retextReadability, {age: 6})

…now running node example.js once moer yields:

  1:1-1:23  warning  Hard to read sentence (confidence: 4/7)  retext-readability  retext-readability
  3:1-5:57  warning  Hard to read sentence (confidence: 7/7)  retext-readability  retext-readability

⚠ 2 warnings


This package exports no identifiers. The default export is retextReadability.

unified().use(retextReadability[, options])

Detect possibly hard to read sentences.


Configuration (optional).


Target age group (number, default: 16). Note that the different algorithms provide varying results, so your milage may vary with people actually that age. 😉


Number of algorithms that need to agree (number, default: 4 / 7) By default, 4 out of the 7 algorithms need to agree that a sentence is hard to read for the target age, in which case it’s warned about.


Minimum number of words a sentence should have when warning (number, default: 5). Most algorithms are designed to take a large sample of sentences to detect the body’s reading level. This plugin works on a per-sentence basis and that makes the results quite skewered when a short sentence has a few long words or some unknown ones.


Each message is emitted as a VFileMessage on file, with the following fields:


Name of this plugin ('retext-readability').


Name of this rule ('readability').


Current not ok sentence (string).


Empty array as there is no direct fix for actual ([]).


Number between 0 and 1 to represent how many algorithms agreed (number).


String representing the fraction of confidence (string, such as 4/7).


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


Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. Our projects sometimes work with older versions, but this is not guaranteed.


See contributing.md in retextjs/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.


MIT © Titus Wormer