Build a grammar checker and writing assistant for professionals and students with these features:
1. A distraction-free editor where users paste or type text and see inline underlines for grammar, spelling, and clarity issues.
2. Issue categorization: correctness, clarity, engagement, and tone, each with a distinct highlight color.
3. One-click fixes per suggestion applied inline, plus an accept-all pass for pure correctness issues.
4. Plain-language explanations for every suggestion so users learn the rule, not just the fix.
5. Tone detection that flags accidental snark, hedging, or formality drift, with rewrite options for warmer or firmer versions.
6. A rewrite menu for selected text or the whole document: simplify, shorten, professionalize, or casualize.
7. Genre presets: email, essay, LinkedIn post, cover letter, and report, each loading its own rules and tone targets.
8. Readability scoring with grade level, sentence length distribution, and passive voice count.
9. Version history so users can compare drafts and roll back a bad rewrite.
10. Personal dictionary where names, product terms, and jargon are never flagged again.
11. Weekly writing stats email: issues caught, most common mistakes, and a readability trend.
12. Freemium paywall: unlimited basic corrections free, with clarity rewrites, tone tools, and genre presets behind a Stripe subscription.