A simple tool to analyse the writing style, word use and readability of prose.

The analysis is produced by the command line tool 'style'.  It performs
several readability tests on the text including; Flesch-Kincaid readability
tests, Automated readability index (aka “ARI”), Coleman-Liau Index, Gunning
fog index (aka "Fog Index"), and SMOG Index (aka "SMOG-Grading", “Simple
Measure Of Gobbledygook“). It also summarises word usage and provides
information about sentence and paragraph structure.

M-x smog-check