Write With Confidence
Catch every grammar mistake, spelling error, and awkward sentence — powered by Harper's lightning-fast engine.
Engineered to bypass every major AI detector
More than a spell-checker
A full writing assistant that catches what others miss.
Deep Grammar Analysis
Catches spelling, punctuation, style, typography, and grammar errors that simple spell-checkers miss.
Real-time Suggestions
Click any highlighted error to see suggested fixes. Apply individual corrections or fix all at once.
100% Private
Your text never leaves your device. Harper runs entirely in your browser via WebAssembly — zero data sent to any server.
Error Breakdown
See a detailed breakdown of issues by category — spelling, grammar, style, and more — so you know where to improve.
Three steps to error-free writing
No learning curve. Paste, review, fix.
Paste your text
Write or paste any text into the editor. Works with articles, emails, essays, and more.
See errors highlighted
Errors are underlined in real-time. Click any highlighted word to see what's wrong.
Accept or dismiss fixes
Review each suggestion, accept it with one click, or dismiss it to keep your original text.
Catches every type of error
From basic typos to complex style issues — nothing slips through.
Spelling
Typos, homophones, and misspelled words
Grammar
Subject-verb agreement, tense consistency, articles, and prepositions
Punctuation
Commas, quotes, dashes, ellipses — get every mark right
Style
Wordy sentences, passive voice, redundancy, and readability
Typography
Smart quotes, correct dashes, non-breaking spaces
Fluency
Awkward phrasing, unnatural word choices, and sentence flow
Frequently asked questions
Everything you need to know before you start.
Powered by Harper — an open-source grammar engine that runs entirely in your browser. It catches grammar errors, spelling mistakes, punctuation issues, and style improvements with zero data leaving your device.
Start checking free — 1,000 words ready
No credit card. No commitment. Just professional-grade grammar checking that stays 100% private.