Grammar checkers (The Scientist, June 27, 1988, page 25) don't check grammar. Some users may find them useful, but like "idea processors" (outline editors) and "desktop publishing systems" (personal typesetting systems), the name is far more ambitious than the product.
Grammar checkers are far from being able to worry about the subtleties of "Time flies like an arrow"; even simple errors like "You knows" or "He has going" or "I want to sheep" (two sheep? to sleep?) are beyond them. They do check for certain hackneyed expressions, overlong sentences, and capitalization errors.
But would they sell if they were called "cliché blacklisters, word counters, and trivial punctuation rule checkers" ? Instead of a "grammar checker," I suggest a few hours' study of Strunk and White's classic The Elements of Style.
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