Grammar Checker

Reliably caught: spelling, homophone confusion (their/there/they're is its bread and butter), subject-verb agreement, double words, casing, many punctuation rules, and style flags like passive voice. Reliably missed: errors that produce grammatically valid sentences with the wrong meaning ('I told him I would meet her' when you meant 'him'), factual mistakes, and tone problems. Rule-based checkers verify rules, not intent — treat a clean result as 'no rule violations,' not 'good writing.'

Not in the way most tools on this site are, and that deserves a straight answer: checking requires sending your text to LanguageTool's servers, where their privacy policy applies (they state texts aren't stored permanently for the free API, but the transmission is inherent to how it works). Practical rule: fine for essays, emails, posts, and anything you'd paste into a web translator; wrong for passwords, unreleased financials, privileged legal text, or anything whose exposure would genuinely matter.

No — and batch-accepting is how writing gets worse. Accept fixes you understand and recognize as errors (typos, agreement, homophones: high confidence territory). Question style suggestions: passive voice, sentence length, and word-choice flags are conventions, not laws, and deliberately breaking them is often the better sentence. When the checker flags something you wrote on purpose, you outrank it. The honest workflow: fix the reds fast, read the style suggestions as a second opinion from a very literal editor.

Different engines and economics. This uses LanguageTool's rule-based open engine — thousands of hand-written grammar rules per language — which is excellent at concrete errors and free without an account. Grammarly layers ML models for tone, clarity rewrites, and flow, behind a subscription and a heavier privacy footprint (browser-wide extensions see everything you type). For catching real errors in a draft, the gap is smaller than the price difference suggests; for full-sentence rewriting, dedicated AI tools are a different category.