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Harper vs Grammarly: catalog facts
Harper	Grammarly
Free Free and open source.	Freemium Free to sign up, with paid plans for more features.
macOS, Web, Browser extension, Command line	Web, Browser extension
All checks run locally with no telemetry Works in browsers, editors and system-wide on macOS	Grammar, spelling and clarity checks as you type One-click paragraph rewrites and tone suggestions
English only Rule-based checks do not rewrite text the way AI assistants do	Requires an account Text is processed on Grammarly's servers
Downloadable app, Web application, Browser extension	Hosted service, Browser extension
Open source	Closed source
License not stated	License not stated
Not stated if an account is needed	Account needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 26, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.