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Privacy policy

Kasan Kurosu works without an account and without ads. We collect a little anonymous data to keep difficulty labels honest and to fix crashes, and you can switch each part of it off.

Last updated 5 October 2026

The short version

  • No ads, no ad networks and no tracking across other apps or websites.
  • You can play every free puzzle without an account. Your progress stays on your device.
  • Anonymous puzzle reports, usage analytics and error reports are each optional. Turn them off in Privacy in the app's Settings.
  • If you sign in, we store your email address so you can keep Pro and your streak on every device. You can export your data or delete your account yourself at any time.

What we collect

Anonymous puzzle reports

When you finish or give up on a puzzle for the first time, the app sends a short report so we can check that each puzzle sits in the right tier. A report contains the puzzle's id and type, whether assistance such as auto-candidates was on, your active solving time, how many hints you used at each step, how many checks and mistakes you made, an outcome score, the app version and the hour of the attempt.

A report has no user id, no device id and no link to an account, and we do not store the IP address it came from. The setting is called Help calibrate puzzles; it is on by default, the app explains it when you first open it, and you can turn it off there or in Settings at any time. Reports wait on your device while you are offline.

Usage analytics

We count which screens and pages get used with Umami, an analytics tool we host ourselves. It sets no cookies, keeps no profile of you and does not follow you to other sites. In the app, turn off Usage analytics in Settings. On this website, Umami respects your browser's Do Not Track setting.

Error reports

When the app crashes or hits an error, it can send technical details (what failed, where in the code, the app version, the browser or device model) to GlitchTip, an error tracker we run. We remove personal data such as email addresses and IP addresses before reports are stored. Turn off Error reports in Settings to stop sending them.

Your account, if you make one

Signing in is optional. If you do, we store your email address and how you signed in (Apple, Google or an emailed link), plus what the account needs to work: whether it owns Pro, your daily puzzle completions and streak, and the devices linked to it. We use your email only to sign you in and to answer you if you write to us. We never send marketing email.

Purchases

Pro is sold by Apple, Google or, on the web, by Paddle, which handle payment. We receive a record that a purchase happened and which account or store account it belongs to. We never see or store your card details.

What we never collect

  • Your location.
  • Your contacts.
  • Advertising identifiers.
  • Device fingerprints.
  • The contents of your boards in analytics.
  • Your keystrokes or recordings of your screen.

Data on your device

Your puzzles, progress, notes, settings and stats are stored on your device (in your browser's storage on the web). Deleting the app, or clearing this site's data in your browser, removes them. If you sign in, your purchase and daily streak are also kept on our servers so they follow you to other devices.

Who processes data for us

We share data only with the services that run Kasan Kurosu for us:

  • Our hosting provider, which runs our servers and database.
  • Cloudflare, which serves puzzle downloads.
  • Resend, which delivers sign-in emails.
  • Paddle, Apple and Google for purchases, and RevenueCat to confirm app store purchases.
  • Apple and Google, if you choose to sign in with them.

We never sell personal data or share it for advertising.

Your controls and rights

  • Turn data sharing off: Help calibrate puzzles, Usage analytics and Error reports are in Settings, under Privacy.
  • Export your data: Export my data, under Account in Settings, downloads everything linked to your account.
  • Delete your account: Delete account, under Account in Settings. Your account and its data are deleted within 24 hours.

Depending on where you live, laws such as the GDPR and South Africa's POPIA give you the right to access, correct, delete or move your personal data, and to object to how it is used. Most of this you can do yourself in the app. For anything else, email support@kasankurosu.com. You can also complain to your data protection authority.

Children

Kasan Kurosu is rated for everyone. It has no chat, no user-generated content and no ads, and it collects nothing extra from younger players. Signing in is never required to play.

Changes

If this policy changes, we will update the date above, and for anything significant we will say so in the app before it takes effect.

Contact

Questions about privacy: support@kasankurosu.com.