Apostrophe Checker
Paste a sentence or a short passage into this tool and it flags the specific apostrophe patterns people get wrong most often: confusing the possessive "its" with the contraction "it's," mixing up a plain plural (dogs) with a possessive (dog's) or a plural possessive (dogs'), and the so-called "greengrocer's apostrophe" — adding an apostrophe to a word that's simply plural and needs no apostrophe at all ("banana's" instead of "bananas"). It's built to catch the small, specific set of apostrophe mistakes that are genuinely common and genuinely rule-based, not to serve as a general proofreading or style tool. If you already understand the its/it's distinction and the plural-vs-possessive distinction in principle but want a fast second pass over a specific paragraph before you send or publish it, this is the right tool; if you want broader feedback on grammar, sentence structure, or style, it isn't built for that and won't pretend otherwise.
Checks only its/it's, your/you're, whose/who's, and plural-vs-possessive apostrophe patterns — not a general grammar or spell checker.
How it works
This tool works by pattern-matching against a defined set of known apostrophe-error patterns, entirely in your browser — it does not call any external grammar-checking API, does not use a large language model, and does not attempt to understand your sentence's full meaning the way a human editor would. Concretely, it looks for specific, well-defined signals: a bare "its" followed by a verb where a contraction ("it's," meaning "it is") would be grammatically required instead, an apostrophe placed before a final "s" on a word that's a common plural noun rather than an actual possessive, and a handful of other named patterns in the same vein. Because it's rule-based rather than model-based, its scope is honest and bounded: it will reliably catch the specific patterns it's built for, and it will just as reliably miss apostrophe mistakes outside that specific list, along with every other kind of grammar or spelling error that has nothing to do with apostrophes at all. It is not, and doesn't claim to be, a full AI grammar checker — if you need broader proofreading, this tool is one narrow, transparent piece of that job, not a replacement for the whole thing. Every flagged instance links back to the relevant rule page — the its-vs-it's page for a contraction/possessive mix-up, the plural-possessives page for a plural-vs-possessive mismatch — so a flag is never just a red mark with no explanation attached; you can always see the actual grammatical reasoning behind why a given pattern was flagged, and decide for yourself whether it genuinely applies to your sentence, since no pattern-based tool can fully account for every legitimate edge case in real writing.
Frequently asked questions
Is this an AI grammar checker?
No. It's a rule-based, client-side pattern checker scoped specifically to apostrophe mistakes — its/it's confusion, plural vs. possessive confusion, and greengrocer's apostrophes. It doesn't use a language model and doesn't attempt general grammar or style checking.
Will it catch every apostrophe mistake?
No tool built on fixed patterns catches every case, and this one is upfront about that: it's built around the handful of apostrophe errors that are most common and most clearly rule-based. Unusual or ambiguous sentences may not be flagged even if they contain a genuine apostrophe error.
Does it check anything besides apostrophes?
No — spelling, comma placement, subject-verb agreement, and every other kind of grammar issue are outside this tool's scope on purpose. It's intentionally narrow rather than a general proofreader.
Is my text sent anywhere when I use this tool?
No. The pattern-matching runs entirely in your browser; nothing you paste in is transmitted to a server or stored anywhere as part of using the checker.
What happens when the checker flags something?
You get a link to the specific rule page behind that flag — for example, the its-vs-it's page — so you can check the actual grammatical reasoning yourself and decide whether the flag genuinely applies to your sentence, rather than being told simply "this is wrong" with no explanation.
Can it flag something that's actually correct?
Yes, occasionally — that's an inherent limitation of a pattern-based checker rather than one that reads full sentence meaning. A flag is a prompt to double-check a specific spot, not a guaranteed error; the linked rule page is there specifically so you can make that final judgment call yourself.