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Harper vs Writing Tools: catalog facts
Harper	Writing Tools
Free Free and open source.	Free Free and open source; cloud model providers may charge separately.
macOS, Web, Browser extension, Command line	Windows, macOS, Linux
All checks run locally with no telemetry Works in browsers, editors and system-wide on macOS	Works on selected text in any application Supports local LLMs as well as cloud APIs
English only Rule-based checks do not rewrite text the way AI assistants do	Needs an API key or a local model set up Output quality depends on the chosen model
Downloadable app, Web application, Browser extension	Downloadable app
Open source	Open source
License not stated	License not stated
Not stated if an account is needed	No 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 26, 2026

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