AI Grammar Checker
Correct grammar, spelling and punctuation — and see exactly what was changed.
Before you use this: These AI tools run on a free Cloudflare allowance, so they are limited to 5 requests per person per day. Every other tool on this site is unlimited — the difference is that those run entirely on your device, while this one needs a server.
Result
How to use this tool
- Select your file, drag it onto the box above.
- Processing starts automatically — there is nothing to configure.
- Check the result panel, which shows the original size, the final size and the page count.
- Click Download to save it.
It returns the corrected text followed by a list of the changes, so you can see what it did rather than trusting it blindly. It is instructed to fix what is wrong rather than rewrite for style.
AI Grammar Checker — the specification
| Input | Up to 6,000 characters |
|---|---|
| Output | Corrected text, then a list of changes |
| Scope | Grammar, spelling, punctuation |
| Limit | 5 per day per person |
| Not included | Style rewriting — use the rewriter for that |
How it works
This is the one part of the site that needs a server. A language model cannot run in a browser at usable speed, so your text is sent to a small Cloudflare Worker, processed at the edge, and returned. The file — where there is one — never leaves your device; only text does.
How it is kept safe and free: there is no API key anywhere, because Cloudflare's AI is bound directly to the Worker rather than authenticated with a token that could be stolen from the page. The prompts live on the server, not in your browser, so the endpoint cannot be repurposed as somebody's free chatbot. An invisible human check and a per-person daily cap keep the shared free allowance available to actual visitors.
Nothing you send is stored, logged, or used for training.
What this page sends, and what the model is told
Every other tool on this site publishes a measured run, because every other tool runs on your device and anyone can reproduce the numbers. This one sends text to a server, and a language model does not give the same answer twice — so printing one response here and calling it a measurement would be dishonest. What can be published exactly is the contract: what leaves your browser, and what the model is told to do with it.
Step one: exactly what is sent
One HTTPS POST, with this body and nothing else. No file, no cookie, no account, no identifier for you:
{
"task": "grammar",
"text": "<the text you typed>",
"turnstile": "<one-time human-check token>"
}
Note what is not in there: the prompt. The browser sends a task name, never an instruction. That is what stops the endpoint being repurposed as somebody else’s free chatbot, and it is why there is no API key anywhere in this page’s source for you to find.
Step two: exactly what the model is told
The server holds the prompt. This is it, verbatim, for this page:
You correct grammar, spelling and punctuation. Return the corrected text first, then a line containing exactly "---", then a short list of the changes you made. Do not rewrite for style; fix only what is actually wrong.
And the message your text is wrapped in:
Correct the grammar and spelling in this text: <the text you typed>
The limits, as the server enforces them
| Model | @cf/meta/llama-4-scout-17b-16e-instruct, on Cloudflare Workers AI |
|---|---|
| Longest text accepted | 6,000 characters — longer is refused, not silently truncated |
| Longest reply generated | 600 tokens |
| Per person, per day | 5 requests, resetting at midnight UTC |
| Whole site, per day | 280 requests, after which the tool stops rather than starts costing money |
| Accepted from | https://onlineaitool.com and https://www.onlineaitool.com only |
Why you should still read the output. The prompt above tells the model not to invent facts, and that instruction helps. It is not a guarantee. Treat what comes back as a draft to check against what you actually know — particularly for anything with a date, a figure or a name in it.
Who needs AI Grammar Checker
Checking an important email, a cover letter, or anything written in a second language before sending it.
AI Grammar Checker — frequently asked questions
Is it as good as a human proofreader?
No. It catches most grammar and spelling errors reliably, but it can miss context-dependent mistakes and occasionally "corrects" something that was right. Review the change list rather than accepting everything.
Does it work for non-native English?
Yes, and that is where it helps most — article usage, prepositions and tense agreement are the errors it catches most consistently.
Is my text sent to a server?
Yes — and this is the one part of the site where that is true. AI needs a model that cannot run in a browser, so your text goes to a Cloudflare Worker, is processed, and comes straight back. It is not stored, not logged, and not used for training. If that matters for your document, use the tools that run fully on your device instead.
Why only 5 uses a day?
The AI runs on Cloudflare's free tier, which gives the whole site a fixed daily allowance. Without a per-person cap, one script could drain it before breakfast and nobody else would get to use it. The limit resets at midnight UTC.
Can I trust the output?
Read it before you use it. Language models produce fluent text that can still be wrong, and they occasionally invent detail. The prompts here explicitly instruct the model not to add facts you did not provide, but treat every result as a first draft to check, not a finished document.
Is this tool really free?
Yes. No account, no trial period, no watermark on the output and no cap on how many times you use it. The site is funded by advertising.
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Background reading: Text and Developer Tools That Never Upload Your Data
Your file never leaves your device. Open your browser's Network tab while you use this page and you will see no upload — how that works.
Disclaimer. AI output is a draft, not a fact-check. Read it before you use it, and never let it invent an employer, a qualification or a number you cannot stand behind. Full disclaimer.