Runs fully offline in your browser using a bundled dictionary and rule set — no text is ever uploaded, logged, or sent to any server, so it works even without an internet connection.
It catches misspellings and common grammar slips (repeated words, spacing, capitalization, a/an, subject–verb agreement, easily confused words like their/there/they're). It's a solid writing aid, not a substitute for careful proofreading — always give your final draft a human read-through.