I have never used a “grammar checker” in a word processing program.* (I can diagram my own sentences quite nicely, thank you.)
Turns out my instincts were correct. At the Hartford Courant, Mark McFadden explains that automated computerized grammar checkers don’t.
*I do use spellcheckers, but never the “automatic” ones. Also, do grade schools still teach grammar, or has it gone the way of civics?