Privacy Policy

Saku: AI-made flashcards, calm study. Last updated: 8 October 2026.

Saku is operated by Tiny Toast Studio LLC ("we", "us"). This policy explains what data Saku handles and why. The short version: your study data is yours, we don't sell it, there are no ads in Saku, and you can erase everything yourself at any time.

What we collect

  • Account: your email address, and your name if you sign in with Google or Apple.
  • Account ID: the identifier of your Saku account.
  • Study content: the cards, decks, topics, tags, guides, AI prompts and card images or photos you create, and your review history (which cards you studied and how you graded them). This powers the spaced-repetition scheduler.
  • Purchases: your subscription and purchase history from Google Play or the App Store, handled through RevenueCat.
  • Usage analytics: how you use the app (screens and actions), linked to your account ID. Our analytics provider stores your IP address and derives an approximate location (country and city) from it. You can turn analytics off in Settings › Privacy & Legal.
  • Ad measurement (Android): your device's advertising ID, an app instance ID and a few app events (first open, sign-up, free trial start and subscription purchase with its price), linked to your account ID. See "Advertising" below.
  • Crash reports and diagnostics: sent when the app hits an error, linked to your account ID.
  • Device push token: used to send you study reminders.
  • Service records: counts of AI, audio and image requests. We use them to enforce fair-usage limits.

How AI features use your content

When you use AI card generation, the material you submit is sent to our AI model provider through OpenRouter to produce your cards. Voice notes and PDF or text files you submit are used only to generate cards. Saku does not store them. When cards have a language set, their text is sent to our text-to-speech providers (Microsoft Azure and Google Cloud) to generate audio clips. Your content is used only to provide these features to you. It is never used to train models on our behalf, and never for advertising.

Advertising

Saku shows no ads. We do advertise Saku itself on Google. To learn which of those ads lead people to install, sign up or subscribe, the Android app uses Google Analytics for Firebase. It collects the ad measurement data listed above, plus an approximate location derived from your IP address, and shares it with Google for ad measurement and attribution in Google Ads. Google handles this data under its own policies for partner apps. We don't use it to show you ads, and we don't sell it. The iOS app doesn't use Google Analytics for Firebase and doesn't access your advertising identifier.

To opt out, turn off Settings › Privacy & Legal › Share usage stats. That stops both PostHog and Google Analytics for Firebase from collecting anything from your device. On Android you can also delete or reset your advertising ID in your device settings (usually Settings › Privacy › Ads › Delete advertising ID; the path varies by device).

Who processes data for us

  • Supabase: database, authentication and file storage
  • PowerSync: synchronising your data across your devices
  • Vercel: application hosting
  • Microsoft Azure and Google Cloud: text-to-speech audio
  • OpenRouter and its AI model providers: AI card generation
  • Sentry: crash reporting and diagnostics
  • PostHog: product analytics linked to your account ID (opt out any time in Settings)
  • Google Analytics for Firebase and Google Ads: measuring our own Google ads on Android (opt out any time in Settings)
  • RevenueCat: subscription and purchase management
  • Google Play / App Store: payments
  • Firebase Cloud Messaging: study reminder notifications
  • Google / Apple: sign-in, if you choose them

Retention and deletion

Your data is kept while your account exists. Deleting your account (Settings › Account › Delete account) permanently erases your account, cards, decks, topics, review history and images from our systems. You can also request deletion at saku.cards/account-deletion. Generated audio for card text is stored in a shared, de-identified cache keyed by the text itself.

Your rights

You can access your data in the app at any time and erase it via account deletion. If you're in the EU/UK or a jurisdiction with similar rights (access, correction, portability, objection), contact us and we'll help.

Children

Saku is not directed at children under 13, and we don't knowingly collect their data.

Changes & contact

If this policy changes materially we'll note it in the app. Questions or requests: hello@tinytoaststudio.com.