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Proton Authenticator vs OTPClient: catalog facts
Proton Authenticator	OTPClient
Free Free and open source under the GPL, with no advertising. A Proton account is used for…	Free Free and open source under the GPL-3.0 license.
Windows, Linux, Android, iOS	Linux, Command line
End-to-end encrypted sync between devices, which most free authenticators lack Apps for Android, iOS, Windows, Linux and macOS	Multiple encrypted token databases Supports TOTP, HOTP and Steam Guard codes
Sync requires a Proton account Keeping codes on the same desktop you log in from weakens second-factor separation	Desktop Linux only, no mobile app Handles one-time codes only, not passwords
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: GPL-3.0
No account needed	No account needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 24, 2026

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