There are certain mathematical formulas, like the Flesch-Kincaid test, that can analyze a document for their “readability level” or the ease at which that document can be read. The score is calculated based on the average number of syllables used per word and the number of words used per sentence.
Readability scores generally help teachers decide if a particular book is suitable for students of a particular grade /age or not.
Readability Level of Web Pages
Earlier, if you were to calculate the readability level of any web page, you would have to copy-paste the text content of that page in a external tool* like Flesh but not any more.
Google has added a new advanced search option that lets you display the readability level of web pages in the search results itself. So if you want to read a page that’s written in simple English, click the result that’s marked as “Basic reading level.”
You can also filter search results in Google by readability level. For instance, set the “reading level” option in Google Advanced Search to “show only basic results” and it should remove pages from search results that may be slightly hard to comprehend.
PS:You could earlier calculate readability scores of documents directly in Google Docs but looks like the features has been dropped now. You can however use Microsoft Word for the same.
Related: Find Errors in your English Writing