Your display name (you choose it, or your first name from Google).
If you use a username and password: the username, and a scrypt hash of the password. The password itself is never stored, and the hash can’t be turned back into it.
If you use Google: a Google account number, so we know it’s you next time. Not your email.
Who you’re linked with.
The video you two are currently on and where you were, so you can pick up where you left off.
Your shared playlists: video links, titles, and which of you added each one. Only the two of you can see them, and they’re deleted if you unlink.
A video one of you has suggested, until the other answers (for up to a day).
Your chat with your partner (the latest 1,000 messages; older ones are deleted for good).
What you’ve watched together, and who picked it (the latest 2,000).
Your sign-in sessions (stored as one-way hashes, so they can’t be stolen from the database).
Only the two of you can see your chat and history. Either of you can clear them at any time, and they’re deleted for good if you unlink or either of you deletes your account.
What we never store
Your email, photo, contacts or location.
Anything you watch on your own. Only videos you both accepted are in your history.
Who can see you
Nobody can search for you. The only way to link is a private invite link you send yourself, and you must approve every request. Only your linked partner sees your name.
YouTube
Videos play in YouTube’s own player, so YouTube’s privacy policy applies to the video itself.
Your control
From your account page you can download your data, sign out everywhere, unlink, or delete your account and everything in it.