Grammar Check guide
A free grammar checker that doesn’t upload your writing
Most grammar checkers send everything you write to their servers. Grammar Check runs Harper, an open-source grammar checker, inside your browser instead: your writing is checked on your own device, mistakes are underlined as you type, and nothing is uploaded. It’s free, with no account.
How a grammar checker works
There are two kinds. Rule-based checkers, like the one in a word processor, split your text into sentences and words, tag each word (noun, verb, article) and run hundreds of rules over them: “a” before a vowel sound, a singular subject with a plural verb, a word typed twice, “should of” for “should have”. AI checkers send your text to a large language model, which suggests rewrites as well as fixes.
Rules are predictable: each underline points at one mistake and says why. They don’t rewrite your voice. AI tools catch more style issues, but usually need your text on their servers.
Where your writing goes
Online checkers and most browser extensions send what you type to their servers to check it, and an extension can see every text box on every page you visit: emails, chats, medical forms, passwords in plain fields. Their privacy policies usually say they keep it for a while and may use it to improve their service.
The mistakes it catches
- Spelling, with suggestions in your English: colour or color, organise or organize.
- Word mix-ups: their, there and they’re; its and it’s; your and you’re; then and than; affect and effect.
- Grammar: “I has”, “a essay”, “should of”, “alot”, a word typed twice.
- Punctuation and capitals: a missing capital at the start of a sentence, spaces before commas, repeated punctuation.
- Style: wordy phrases and needless repetition, which you can turn off.
Check your writing, step by step
- Open Grammar Check and tap Paste and check, or start a new document and type.
- Mistakes are underlined as you go: red for spelling, orange for grammar, purple for punctuation, blue for style.
- Tap an underline to see what’s wrong in plain words, then tap the fix. Your browser’s undo brings the old word back.
- Names and brands it doesn’t know: tap Add to dictionary. Something you meant on purpose: tap Ignore.
- Open the issues list to see everything at once and go through it in order.
What it won’t do
It doesn’t rewrite sentences, change your tone or write for you: it points out mistakes and offers fixes. It checks English only. And no checker catches everything, so read important writing aloud once before you send it; it’s the best proofreading trick there is.
Questions
Is it really free?
Yes. Every check and every fix is free. Grammar Check Pro ($1.99 once) adds unlimited documents, Fix all at once and an unlimited dictionary.
Does it work offline?
Yes, once the checker has downloaded the first time.
Does it do British English?
Yes: American, British, Australian, Canadian and Indian English, in Settings.
Where are my documents kept?
In your browser on this device only. Clearing the site’s data removes them.