I’m not a fan of those apps and checkers that purport to “fix” your writing. They get way too hysterical about choices that should be judgment calls (e.g., starting a sentence with “But”). Here, however, is a useful list of common-sense sources to help with grammar conundrums. Thanks to Melissa Donovan, and to Chris the Story Reading Ape for sharing it.
(Forgive a moment’s rant about people I see on various self-help social-media pages who claim that they can be good writers while dispensing with a thorough understanding of the “grammar rules.” Some of these “rules” are flexible, but some basic punctuation conventions and sentence-structure mandates like subject/verb agreement are not. Yes, commas can be tricky, and we can argue about which ones are needed and which are optional, but if you still don’t know where apostrophes belong and where they don’t. . . . Yes, there really are grammar police. They’re called agents. 😦 )