A grammar checker that never sees your text
Most online grammar checkers send everything you type to a server. This one doesn’t. It runs Harper, an open-source grammar engine written in Rust and maintained by Automattic, compiled to WebAssembly and executed in a background thread inside your browser. The first visit downloads the engine (about 8 MB compressed); after that it loads from your browser’s cache and keeps working offline.
That makes it suitable for contracts, medical or HR documents, student work and unpublished writing, and there is no character limit, account or daily quota.
What it checks
- Spelling and typos, in American, British, Canadian, Australian or Indian English.
- Grammar and agreement: “I has”, “a apple”, “could of”, subject–verb mismatches and many fixed-phrase errors.
- Commonly confused words, eggcorns and malapropisms (“for all intensive purposes”).
- Punctuation and capitalisation, including repeated words and spacing.
- Style and redundancy: wordy or redundant expressions and some clichés.
Click a suggestion to apply it, Ignore to hide it for this session, or click the issue to jump to it in your text. Tick Text is Markdown to skip code blocks and link URLs.
What it won’t do
Harper is a rule-based engine, not a large language model. It is fast and predictable, and it doesn’t invent rewrites, but it also won’t restructure a confusing paragraph or judge your argument. Combine it with the Clarity Checker for long or tangled sentences and the Readability Checker for overall difficulty. No automated checker catches everything; read important work aloud before you send it.
Questions
Is this grammar checker really free?
Yes. There is no account, no premium tier for the checker and no word limit. Because it runs on your device, it costs us nothing extra when you use it more.
Is my text sent anywhere?
No. The grammar engine runs inside your browser in a Web Worker. Your text never leaves your device. You can verify this in your browser’s network panel.
Why is the first load slower?
The engine and its dictionary are downloaded once (about 8 MB compressed) and cached. Later visits start almost instantly, even offline.
How does it compare with Grammarly or LanguageTool?
It is faster, private and unlimited, and it catches the common spelling, grammar and word-choice mistakes well. Commercial AI tools offer rewriting and tone suggestions that a rule-based engine does not attempt.
Can I check British English?
Yes. Choose British, Canadian, Australian or Indian English from the variety menu; spellings like “colour” and “organise” are then accepted.
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