A spell checker compares each word against a dictionary. That catches typos and nothing else, which is why "their", "there" and "they're" sail through untouched. All three are real words, spelled correctly, and only the surrounding sentence reveals which one belongs.
How grammar checking differs
A grammar checker works on sentences rather than words. It identifies the likely part of speech for each word, then applies rules about how those parts fit together. Seeing a possessive determiner where a location adverb is needed, it flags "their" and suggests "there".
Most practical checkers, including LanguageTool, combine a large hand-written rule set with statistical patterns learned from real text. Rules catch clear-cut errors precisely; statistics catch things nobody thought to write a rule for.
What it catches reliably
- Subject-verb disagreement: "the list of items are" should be "is".
- Confused homophones: their/there, your/you're, its/it's, affect/effect.
- Doubled words across a line break, which eyes skip over easily.
- Punctuation around quotes and parentheses, and missing apostrophes in contractions.
- Article errors: "a hour", "an university".
- Spacing mistakes before punctuation and inconsistent dash usage.
What it misses
Anything requiring knowledge of what you meant. A sentence can be grammatically flawless and still wrong: a name misspelled as another valid name, a negation accidentally reversed, a figure that contradicts the paragraph above. The checker has no idea what you intended to say.
It also has no sense of your audience. It cannot tell you that a sentence is too formal for a text message, that a paragraph buries its point, or that an idea has been repeated three times in slightly different words. Those are editing decisions, not grammar.
False positives are normal
Checkers over-flag specialised writing. Technical terms, product names, deliberate sentence fragments and unusual constructions all trigger warnings that are not errors. Treat every suggestion as a question rather than an instruction: the checker noticed something unusual, and you decide whether it is wrong.
Accepting every suggestion uncritically tends to flatten writing into something more correct and less clear.
Why your text has to be sent somewhere
Grammar checking needs a large rule set and language model, far too heavy to download into a browser tab for a quick check. That is why nearly every free grammar checker, including this one, sends your text to a server.
It is worth being conscious of that. Our checker sends text only when you press the Check button, so you can type and edit freely beforehand, but the text does leave your device at that moment and is handled under LanguageTool's privacy policy. For an unreleased contract or anything confidential, use offline software.
Getting the most out of it
- Write first, check afterwards. Checking as you type interrupts the sentence you are forming.
- Read each suggestion rather than accepting it in bulk.
- Read the text aloud afterwards. Awkward phrasing is audible in a way it is not visible.
- Keep a note of mistakes you repeat, since those are worth learning rather than re-fixing.