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