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proselint vs Harper: catalog facts
proselint	Harper
Free Free and open source under the BSD 3-Clause licence.	Free Free and open source.
Windows, macOS, Linux, Command line	macOS, Web, Browser extension, Command line
Checks based on established usage guides and editors Works on plain files from the command line	All checks run locally with no telemetry Works in browsers, editors and system-wide on macOS
English only No graphical interface	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: BSD-3-Clause	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 October 2, 2026	Official website Full listing and sources Checked September 26, 2026

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