Less than Perfect
I stumbled across a web site which offered to be my "personal grammar coach". Just what I needed! They allow you try the service (in a limited capacity) by pasting a section of text in the box. I copied a few FITK posts and received various "ratings" from 60 to 70 percent of what I assume to be "perfection".
Just to make sure the service was legit, I pasted some excerpts of F. Scott Fitzgerald short stories. They did worse! I made one final test—with the final paragraph of Poe's The Tell Tale Heart. It got 82% and would have probably gotten 100% if it hadn't been discounted for its use of archaic language.
It looks as if my writing has a ways to go.