This extension provides a quick-and-easy display of the readability score of text in plain text or Markdown files when a file is opened or saved, or when the "Check readability" command is run (Ctrl + Shift + P, "Check readability").

Currently supported readability score formulas include:

• Automated Readability Index
• Coleman-Liau Index
• Dale-Chall Readability Formula
• Flesch Reading Ease
• Flesch-Kincaid Grade Level
• Simple Measure of Gobbledygook (SMOG) Formula

Currently supported languages include:

• Plain text files
• Markdown

Future plans for this extension include highlighting the text based on readability score values (eg: long sentences, difficult paragraphs, challenging words, etc.) to make it easier to see where the text could be revised.

Text is reviewed using the Automated Readability Index formula, and calculates the approximate US grade level needed to understand the text, based roughly on the length of words in the document and the number of words per sentence.

The returned score can be from 1 to 14, and will generally represent the grade level required to understand the text. More specifically:

Text is reviewed using the Coleman-Liau index, which calculates the approximate US grade level needed to understand the text. The Coleman-Liau index relies on characters instead of syllables per word, much like the Automated Readability Index.

The returned score is an integer above 1, and will generally represent the grade level required to understand the text, with level 14 and above being suitable for a college student.

Using the Dale-Chall Readability Formula, the text is checked against a list of 3,000 words that fourth-grade American students should be able to reliably understand, and any words in the text that are not on that list are marked "difficult." The final score is generated taking into account the percentage of difficult words in the text and the number of long sentences.

The final score can be any number below 9.9, and corresponds roughly to the following grade levels:

The familiar words list is provided by the dale-chall library released under MIT license by Titus Wormer.

Using the Flesch Reading Ease formula, the text's readability score is generated in part based on the average number of words in sentences, and the average number of syllables in the words.

The returned score can be from negative numbers to 120. These can be roughly approximated to the following grade levels:

The syllable count is generated using the syllable library released under MIT license by Titus Wormer.

The score is calculated using the Flesch-Kincaid grade level, which determines readability based on the average number of words in sentences, and the average number of syllables in the words. That score is then translated into the approximate grade level required to understand the text.

The returned score is the approximate grade level required to understand the text; or, the number of years of education required to understand the text (especially when the formula returns a number higher than 10). Negative numbers are possible, but usually indicate the text is very easy to read.

The syllable count is generated using the syllable library released under MIT license by Titus Wormer.

The SMOG Formula uses the number of sentences and the number of polysyllabic words in the text to generate the approximate number of years of education needed to understand the text.

The syllable count is generated using the syllable library released under MIT license by Titus Wormer.

Using the Spache Readability Formula, the text is checked against a set list of everyday words, and any words in the text that are not on that list are marked "difficult." The final score is generated taking into account the percentage of difficult words in the text and the average sentence length.

The score returned by the formula will reflect the approximate grade level that should be able to understand the text.

The Spache readability formula is best used on texts that are targeted to younger audiences (children in or below 4th grade). For older audiences, the Dale-Chall formula will generally work better.

The familiar words list is provided by the spache library released under MIT license by Titus Wormer.

This extension supports the following settings:

• readabilityCheck.formula: determines which algorithm to use for scoring

Score can be any of the below options:

• automated-readability, for the Automated Readability Index score
• flesch, for Flesch Readability Ease
• flesch-kincaid, for the Flesch-Kincaid US Grade Level
• coleman-liau, for the Coleman-Liau Index
• dale-chall, for the Dale-Chall Readability Formula
• smog, for the Simple Measure of Gobbledygook (SMOG) Formula
• sprache, for the Sprache Readability Formula

If unset, the extension will default to automated-readability.

Initial release of ReadabilityCheck

Add Markdown format stripping to make the wordcount/character counts more accurate, to improve score accuracy.

Update extension to add user settings options.

Fix wordcounts and word list parsing to improve accuracy for Dale-Chall, Coleman-Liau, and SMOG formulas

This extension is released under the MIT license.

This extension references the following packages released under the MIT license:

• syllable, developed by Titus Wormer
• dale-chall, developed by Titus Wormer
• spache, developed by Titus Wormer
• remove-markdown, developed by Stian Grytøyr