Word Count Tool от Harry N.

This add-on reports the number of words, characters of the selected text, including the number of words, characters, characters without spaces, sentences, paragraphs, Mean Word Length, Mean Sentence Length is easily accessed by one of the following ways:
- Right clicking to view the context menu (when there is some text selected), and choose Word Count Tool item.
- Using hot key combination: Alt + Shift + C

The web version of this tool is also available at https://wordcounttools.com.