Privacy Policy

Last updated: July 2026

Red Thread Labs LLC ("we", "us", "our") makes the duiduidui! application and related services (the "Service"). This Privacy Policy explains what information we collect, how we use it, and the choices you have. If you have questions, email us at privacy@duiduidui.app.

1. Information we collect

We collect the following categories of personal information. The mapping to Apple's privacy-nutrition-label categories is noted in parentheses.

Information you provide directly

  • Email address or phone number (Contact Info). Optional. Used to sign in with a one-time code and to recover your account on a new device. You can use the Service in an anonymous trial state without providing either.
  • Display name, username, and profile photo (Name; Photos or Videos). Optional. Used to identify you to friends inside the Service.
  • Messages you send to our AI tutor (Other User Content). Used to generate a response and improve the Service.
  • Content you create in the app (Other User Content). Your starred dictionary entries, flashcard progress, study sessions, and tags. Stored so you can pick up where you left off across devices.
  • Dictionary search history (Search History). The dictionary searches you perform are saved as a recent-search list so you can revisit and step back through them, synced across your devices. The searches themselves run on-device against the offline dictionary; only the saved history is associated with your account.

Information collected automatically

  • Account identifier (User ID). We generate a random account ID for you on sign-up. This ID is used to associate your data on our servers. It is not your Apple ID, IDFA, or any other device identifier.
  • Purchase and subscription history (Purchase History). When you subscribe through the App Store, Apple provides us with an original transaction identifier and subscription status. We do not receive your payment details.
  • Product interaction and diagnostics (Product Interaction; Performance Data; Crash Data; Other Diagnostic Data). We log how you use the app: which dictionary entries you open, which entries you play audio for, and which flashcards you review and the grades you assign, along with general usage events (screen transitions, feature usage), API latencies, errors, and crashes. These events are recorded with your account ID, device model, OS version, and app version. We use them to operate the Service (for example, to power your study history and tune the adaptive review system) and to understand and improve how the app is used. We do not use this information to track you across other companies' apps or websites, and we do not sell it.
  • Website analytics (Product Interaction). On our website (duiduidui.app), we use Google Analytics to understand site traffic in aggregate: which pages are viewed, how visitors arrive, approximate geography (city or region), and browser and device type. Google Analytics sets cookies to distinguish visitors, and Google processes technical data such as your IP address to provide the service. This applies to the website only, not the app, and we do not use it for advertising or cross-site tracking.

Information we do not collect

  • We do not collect precise or approximate location.
  • We do not collect your contacts or address book.
  • We do not collect health, fitness, or browsing history.
  • We do not use the advertising identifier (IDFA) or any cross-app / cross-site tracking.

2. How we use your information

We use your information to:

  • Operate, provide, and improve the Service (including dictionary lookups, flashcard reviews, and AI tutoring).
  • Authenticate you and keep your account secure.
  • Sync your learning progress across devices.
  • Process your subscription and restore purchases.
  • Deliver one-time verification codes by email or SMS.
  • Diagnose and fix crashes and performance problems.
  • Understand how the Service is used in aggregate so we can make it better.
  • Respond to your questions or reports and enforce our Terms of Service.
  • Meet legal obligations.

We do not use your personal information for third-party advertising, for cross-app or cross-site tracking, or to sell to data brokers.

3. Who we share information with

We share personal information only with service providers who help us run the Service, and only to the extent they need it to do their job. Our current service providers include:

  • Apple: App Store, in-app purchases, server-to-server notifications about your subscription status.
  • Amazon Web Services (AWS): hosting, database, image and audio storage.
  • Anthropic: powers our AI tutor. When you send a message in the tutor, the message text (not your email, phone, or name) is sent to Anthropic to generate a response.
  • OpenAI: generates the synthesized speech audio for dictionary entries. Only the text to be spoken is sent; no personally identifying information.
  • Superwall: manages the subscription paywall. To decide when and how to show subscription offers, we send Superwall app-usage and learning-progress signals (for example, how recently and how much you've studied, your current study streak, an estimate of your skill level, and your subscription status), but not your name, email address, or phone number. Superwall's own SDK also collects standard device and app information. It relays Apple transaction identifiers back to us.
  • Brevo: sends one-time verification codes by email.
  • Google: website analytics (Google Analytics) on duiduidui.app, used to understand aggregate site traffic.
  • A telephony provider (such as Twilio): sends one-time verification codes by SMS, where applicable.

We may also disclose information:

  • When you direct us to (e.g., sharing progress with a friend).
  • To comply with applicable law, lawful requests, or legal process.
  • To protect the rights, property, or safety of Red Thread Labs LLC, our users, or the public.
  • In connection with a merger, acquisition, financing, or sale of assets, subject to customary confidentiality protections.

We do not sell your personal information.

4. Connecting third-party AI assistants

You can choose to connect duiduidui! to third-party AI assistants (for example, Claude) so that they can access your learning data on your behalf. This is entirely optional and off by default; it happens only when you explicitly authorize a connection.

  • How it works. Connections use the OAuth 2.0 standard. When you authorize an assistant, you grant it a limited set of permissions ("scopes"), and we issue it a revocable access credential. We never share your password, email address, or phone number with the assistant.
  • What it can access. Access is limited to the scopes you grant. The available scopes cover: your dictionary entries and saved vocabulary, your flashcard study sessions and review history, your profile and learning summary (including subscription and billing status), your past AI-tutor chats, your social connections, and the ability to add or update your own vocabulary entries. An assistant can only reach the categories you approve.
  • Where your data goes. When a connected assistant requests your data, we send the requested information to that assistant. Once it leaves duiduidui!, that data is handled under the third party's own privacy policy and terms, not this one. Review their policies before connecting.
  • Staying in control. You can review your active connections and revoke any of them at any time from the "Connected AI Assistants" screen in the app's Settings. Revoking a connection immediately stops further access.

5. International data transfers

We operate from the United States, and our service providers are located in the United States and other countries. If you use the Service from outside the United States, your information will be transferred to, stored, and processed in countries whose data-protection laws may differ from those where you reside. By using the Service you consent to this transfer.

6. How long we keep your information

We keep your account information for as long as your account is active. When you delete your account, we delete the associated personal information within a reasonable time, except where retention is required by law (for example, financial records relating to subscriptions) or needed to resolve disputes, enforce our agreements, or preserve the integrity of backups and logs. Operational logs and diagnostic records are retained for up to 13 months.

7. Your choices and rights

You can:

  • Skip sign-up and use the Service anonymously for a limited time.
  • Add or remove contact information (email and phone) at any time in the app's Profile tab.
  • Edit your display name, username, and avatar in the app's Profile tab.
  • Cancel your subscription through your Apple account settings.
  • Delete your account. Use the "Delete Account" action in the app's Settings, or email privacy@duiduidui.app.

Depending on where you live, you may have additional rights under laws like the European Union's General Data Protection Regulation (GDPR), the United Kingdom's UK GDPR, or the California Consumer Privacy Act (CCPA). These may include the right to access, correct, delete, port, or restrict our use of your personal information, or to object to certain processing. To exercise any of these rights, email privacy@duiduidui.app. We will respond within the timeframes required by applicable law.

We do not discriminate against you for exercising any privacy right.

8. Children's privacy

The Service is not directed at children under 13, and we do not knowingly collect personal information from children under 13. If we learn that we have collected information from a child under 13 without a parent's consent, we will delete it. If you believe a child has provided us with personal information, please contact privacy@duiduidui.app.

9. Security

We use industry-standard technical and organizational measures to protect your information, including encryption in transit, access controls, and secure credential storage on your device (Apple Keychain). No system is perfectly secure, and we cannot guarantee absolute security.

10. Third-party links and services

The Service may link to or interoperate with third-party sites and services (for example, the Apple App Store). Their privacy practices are governed by their own policies. We are not responsible for those practices.

11. Changes to this Privacy Policy

We may update this Privacy Policy from time to time. When we make material changes, we'll let you know in the app or by email. Continued use of the Service after the effective date means you accept the updated policy.

12. Contact us

Questions, requests, or concerns about this Privacy Policy should go to:

Red Thread Labs LLC privacy@duiduidui.app