Optional: practice works without an account. Without one, your progress stays on this device only and may be lost, for example when browser data is cleared. With one, your passed levels and each level's best result are saved on the server and synced across your devices. We email you only to confirm your address or to reset your password.
Signing up or in moves what this browser shared (score timelines, challenges, results and matches) and its progress to the account. Stored: your email address, whether it is confirmed and a password hash, kept until you delete the account. Our emails (a confirmation or reset link) go through Cloudflare's email service, which receives your address and the message.