Before letting anyone else see your writing for the first time, it's always a good idea to run a spelling and grammar check. For a project the size of a novel, this generally means clicking Ignore several hundred times to ferret out a few dozen mistakes. Note that by this point I've reread the thing multiple times, checking all the red squigglies as I go; don't think for a second my first draft doesn't have a lot more mistakes than that.
I'm probably not the only one, but when I write I make choices that the spellchecker doesn't always agree with. Creative names, an accent that calls for innovative spelling, (parenthetical clauses the spellchecker can't follow), and cutting short a spoken sentence--all of these can bring out a swarm of red or blue squigglies. Most of what spellcheck flags can be chalked up as a difference of opinion. For the record, I'm looking at red squigglies under the word "squigglies" right now ... and I'm okay with that.
The grammar checker, though, now that one can be fun. More than just suggested improvements that I'm declining out of some sense of artistic freedom, in many cases it's flat-out wrong, sometimes outrageously so. I know the tool has gotten better over the years. Back in the late nineties I remember a version that would throw out objections like, "This sentence does not appear to have a verb," even when it clearly did. I told myself one day I'd run some great works of literature through a grammar checker and reprint the most hilarious annotations as it corrected Hemingway or Steinbeck, Fitzgerald or Salinger. (I was about to throw out a name like Joyce, but we already know his grammar is intentionally broken; that's part of his charm, so using him wouldn't be playing fair. Same for Kerouac, or even the heavily accented dialogues of Twain.)
But that was nearly two decades ago, and I still haven't managed to get around to the project, so in the stead of laughing at grammar check failing to handle fine literature, I'll use my own writings instead.
We'll start small. Very small: it's. According to the stats, I used "it's" 319 times in my upcoming novel, tentatively titled The Eight-Bit Bard. Of those instances, spellcheck is convinced 11 cases ought to be its instead. These include selections like, "It's okay," "You think it's poison?", "I don't think it's working," "It's part of the job," and "It's his map." All of these cases I do mean it is, and not "belonging to it." Oddly, the software never once flagged one the other way around.
Did it have some troubles with statements and questions? It did. "Next to him lounged a halfling in reinforced leather" doesn't need to end in a question mark, no matter how much grammar check begs. Likewise for "I was happy to let him have it."
Since this is fantasy, I can see how it might try to replace the word "mages" with "images" occasionally, but that's not going to improve the story. And while "I was a bard back then" might trigger the same skepticism, trying to replace it with "I was a bad back then" isn't helping. And, frankly, "I could see a rend in the ectoplasm" is not secretly supposed to be a trend in the ectoplasm. My characters are adventurers, not business analysts, by Infernus.
As for pronoun-verb agreement, I think grammar check has been taking notes from my four-year-old, who still starts sentences with "him went" or "us are". Suggested corrections included, "I was willing to grant the idea that, on a purely aesthetic level, man-flesh tasted much well than troll flesh," "Don't let they touch you," "Teleport we back outside," and the surprisingly simple, "Neither did me."
Homophones are knot just for humans. Grammar check suggested that rather than a whine, the dog sank to the ground with a wine; I cannot tell you know came over me; combat broke lose; and the dwarf has got away with people. The computer has got a way with words, for sure.
Saving the best song for last: who wouldn't want a finely tuned arm, rather than a finely toned one? Right?