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HARPA AI vs Sider: catalog facts
HARPA AI	Sider
Freemium Free to install, with paid plans for heavier use of hosted models.	Freemium Free to start, with paid plans for more usage.
Browser extension	Windows, Android, iOS, Web, Browser extension
Works with many AI providers and local models YouTube, PDF and page summaries in place	Access to several AI models in one sidebar Page summaries and notes while browsing
Mainly a Chrome extension Hosted models send page content to third-party AI providers	Closed source hosted service Heavy use needs a paid plan
Browser extension	Downloadable app, Web application, Browser extension
Closed source	Closed source
License not stated	License not stated
Not stated if an account is needed	Not stated if an account is needed
Needs internet	Needs internet
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 23, 2026

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