How to use it
- Type or paste your text, or open a TXT, DOCX or PDF file.
- Choose your English: American, British, Australian, Canadian or Indian.
- Click an underlined word to see the explanation and suggestions on the right.
- Click a suggestion to apply it, or Ignore to hide the issue.
What it catches
Harper checks your text against hundreds of rules, including:
- Commonly confused words: their/there/they're, its/it's, then/than, affect/effect, alot → a lot.
- Agreement: he go → he goes, a apple → an apple.
- Spelling: typos and mixed American/British spellings (color/colour).
- Word choice and style: doubled words (the the), a missing capital at the start of a sentence.
- Punctuation: some missing commas (for example after However at the start of a sentence), double spaces.
Each underline color stands for a category, and the panel explains each issue in plain English.
Privacy and limits
Most online grammar checkers send your text to a server. This one downloads the Harper engine (about 8 MB the first time, then cached) and checks everything on your device, so confidential documents stay private. Harper is rule-based: it's fast and predictable and never rewrites your sentences, but it can miss some complex errors that an AI rewriter or a human proofreader would catch, such as a wrong tense deep inside a long sentence. It checks English only.
Frequently asked questions
Is this grammar checker really free?
Yes – no account, no word limit and no premium upsell for the checks.
Is my text stored or uploaded?
No. The grammar engine runs as WebAssembly in your browser. Your draft is kept in this browser only.
Does it support British English?
Yes. Choose American, British, Australian, Canadian or Indian English and the suggestions follow that dialect.
Is it a Grammarly alternative?
For grammar and spelling, yes – free and private. It doesn't rewrite sentences or suggest tone changes.