A readability score is a computer-calculated index that helps technical writers learn what level of education a reader will need to understand a text easily. Readability really matters since tech writers should write user-oriented documentation that users will gladly read. Moreover, search engines like Google also care. Google has publicly stated that readability is one of the factors in its ranking algorithm. That’s why the readability score also helps you improve SEO.
ClickHelp provides you with a number of readability metrics. For example, Flesch Reading Ease, Gunning Fog Index, New Dale-Chall Formula and so on. You can learn more here: Readability Metrics.