Every "free" grammar checker eventually asks for something — an account, a browser extension, a word cap that kicks in right when you're checking something that actually matters. I tested 5 tools specifically against the no-signup, no-extension bar: paste text, get corrections, done.
1. ToolTiny — LanguageTool's engine, zero setup
ToolTiny's Grammar Checker runs on the public LanguageTool API — the same open-source grammar engine that powers LanguageTool.org itself — wrapped in a simpler interface with no account step at all. Paste text, pick from 20+ languages (or let auto-detect handle it), click check, and click through green suggestion buttons to apply fixes one at a time. Text is sent over an encrypted connection for processing and isn't stored afterward.
Worth knowing since it's built on LanguageTool's public API specifically: character limits and rate limits follow whatever LanguageTool's public tier allows at any given time, not a ToolTiny-specific cap. For very long documents or heavy daily use, that's the practical ceiling to be aware of — same engine, but accessed through the free public tier rather than a paid or self-hosted one.
2. LanguageTool — the engine itself, with a higher free ceiling and self-hosting
Going straight to LanguageTool.org gets you a 10,000-character limit per check on the free tier — noticeably more headroom than most competitors — plus the option to self-host the open-source engine entirely if you need text to never leave your own infrastructure. If ToolTiny's public-API ceiling is the constraint, this is the direct upgrade path using the exact same underlying technology.
3. Grammarly Free — the widest ecosystem, most restricted feature set
Grammarly's free browser extension remains the most widely deployed grammar tool by a large margin, and it works everywhere you type online — email, docs, social posts — not just in a dedicated text box. The trade-off on the free tier is feature access rather than a hard character cap: deeper style, tone, and clarity suggestions sit behind the paid plan.
4. QuillBot — grammar checking plus in-line rewriting
QuillBot bundles grammar checking with contextual AI commands to rewrite, simplify, or expand flagged sentences directly in the editor, rather than just flagging the problem and leaving you to fix it. Free, no signup required, with browser and desktop app options if you want it available system-wide.
5. Scribbr — built for academic writing, no published limit
Independent testing has found Scribbr's free checker catching close to the top error-detection rate among no-signup tools, and unlike several competitors, it doesn't publish a free-tier length cap. It leans toward an academic-writing audience — citation-adjacent tools live alongside it — which shows in how conservatively it flags style versus hard grammar errors.
Quick comparison
| Tool | Character limit (free) | Account needed | Best for |
|---|---|---|---|
| ToolTiny | Follows LanguageTool public API | No | Fast check, 20+ languages, zero setup |
| LanguageTool | 10,000 chars, self-host option | No (free tier) | Long documents, privacy-critical text |
| Grammarly | No hard cap, features gated | No (free tier) | Checking everywhere you type, not just one box |
| QuillBot | No signup required | No | Wanting rewrite suggestions, not just flags |
| Scribbr | No published limit | No | Academic papers and essays |
Which one for which situation
- Quick check on a short piece, don't want to think about it? ToolTiny — paste and go, no setup.
- Checking something long or genuinely confidential? LanguageTool directly, for the higher free limit or self-hosting.
- Want grammar-checking everywhere you type, not just one page? Grammarly's browser extension.
- Want the tool to rewrite the sentence, not just flag it? QuillBot.
- Proofreading an academic paper? Scribbr.
The honest note
A grammar checker catches what a rule-based or statistical model can detect — subject-verb agreement, common misspellings, missing commas, awkward phrasing. None of them, including the ones with "AI" in the name, reliably catch a sentence that's grammatically perfect but factually wrong, or a tone that's technically correct but reads as rude in context. Independent testing across these tools consistently finds none of them catch everything, which is exactly why the standard advice — read your writing out loud before sending it — still holds even after running it through the best free checker available.
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