What Free Grammar Checkers Catch, and What They Miss
Free grammar checkers catch agreement, tense and homophones. They miss meaning, contradiction and structure — and flag correct writing constantly.
A free grammar checker will catch the errors that make writing look careless. It will not tell you whether the sentence is any good, and it will confidently flag things that are perfectly correct.
Knowing which is which is the difference between a useful tool and one that slowly makes your writing worse.
Grammar Checker
Paste a draft and get corrections. Best used as the last pass, after the structure is settled.
What it reliably catches
- Subject–verb agreement — “the list of items are” when it should be “is”.
- Tense drift inside a sentence or paragraph.
- Homophones spellcheck sails past — their/there/they’re, its/it’s, your/you’re, affect/effect in clear cases.
- Comma splices and run-on sentences.
- Missing or doubled articles — the commonest error for writers whose first language has no articles.
- Doubled words across a line break, which the eye reliably skips.
These are worth catching precisely because you cannot catch them yourself. You read what you meant to write, not what is on the page.
What it misses
Everything that depends on meaning.
- The right word used wrongly. If both readings parse, no checker can tell which you meant.
- Contradiction. A paragraph that undoes the one before it is grammatically flawless.
- Factual error. “The Battle of Hastings was fought in 1067” passes every check.
- Structure. A piece in the wrong order reads badly sentence by sentence perfectly.
- Saying nothing. The most common fault in published writing, and entirely invisible to a grammar tool.
Worth remembering. A grammar checker measures whether sentences are well formed. It has no opinion on whether they are worth reading — and a page of immaculate, empty sentences is a worse outcome than a rough page that says something.
Why it flags correct writing
Style rules dressed as grammar. Passive voice, sentence length, starting a sentence with “But” or “And”, ending with a preposition — these are preferences, and several are outright myths. A checker trained on formal prose will flag good conversational writing all day.
Passive voice in particular gets flagged reflexively, and it is often the right choice: when the actor is unknown, irrelevant, or deliberately de-emphasised. “The file was corrupted” is better than inventing a culprit.
Missing context. Proper nouns, product names, technical terms and deliberate fragments all look like errors. “n8n” is not a typo. A one-word sentence for emphasis is a choice. Really.
The habit worth building: if the suggested fix makes the sentence stiffer, longer or less like you, decline it. Accepting every suggestion is how writing ends up sounding like a corporate style guide.
British and American English
Most tools default to American spelling, so colour, organise, centre and travelled get flagged in text that is entirely correct. That is a locale setting rather than a mistake.
The rule that matters more than which you choose: be consistent. A page mixing optimize and colour reads as carelessly assembled — which is precisely the impression correct grammar is supposed to prevent.
The order that works
Checking grammar while drafting is the slowest way to write. You break off mid-thought to fix the sentence behind you, and the piece never builds momentum.
- Draft. Get the argument down. Accept that it is rough.
- Structure. Is anything missing, repeated, or in the wrong order? The summariser is useful here — if a summary of your own piece misses your main point, your structure is burying it.
- Line edit. Fix the clumsy sentences yourself; use the paraphrasing tool on the ones that resist.
- Grammar. Now. There is no point polishing a paragraph you are about to delete.
- Read aloud. Catches rhythm problems no checker sees.
Does grammar affect SEO?
Not directly. Google has said repeatedly that spelling and grammar are not ranking factors in themselves.
Indirectly, it matters a good deal. Google’s own guidance on helpful content asks whether a page appears well-produced or sloppy, and whether it would be trusted — and error-strewn writing fails that test with readers before it fails with an algorithm. People leave, and leaving is measurable.
Questions worth asking
Are free grammar checkers good enough?
For catching real errors, yes. Paid tools mainly add style scoring, tone analysis and integrations — useful for teams enforcing a house style, unnecessary for most writing.
Should I accept every suggestion?
No, and doing so is the main way these tools damage writing. Take the corrections, weigh the style advice, and decline anything that makes a sentence less like you.
Is my text private?
This tool sends your text to an AI provider to generate corrections. Nothing is stored on this site, but the text does leave your device — so do not paste anything confidential or client-privileged. If you want something that never transmits anything, the word counter and case converter run entirely in your browser.