Privacy Policy

Last updated: July 5, 2026

HanziDiff (“we”, “us”, the “App”) is a Chinese vocabulary learning app for learners of Chinese. We keep data collection to the minimum needed to run the service. This policy explains what we collect, why, and the choices you have.

Information we collect

• Anonymous device identifier. When you first open the App, it generates a random device ID stored on your device. We use it to deliver the daily puzzle, keep your free daily allowance, and prevent abuse. It is not your Apple ID and does not identify you personally.
• Apple account (optional). If you choose Sign in with Apple, we receive an opaque Apple user identifier (and a relay email only if you choose to share one). We never receive your Apple password.
• Your submissions. The answers you write — in English or in Chinese — are sent to our server and to an AI model to generate scoring and feedback.
• Purchases. Subscriptions are processed by Apple. We receive transaction identifiers from Apple to unlock Pro features. We never receive your payment card details.
• Device integrity (App Attest). For anonymous scoring we use Apple’s App Attest to confirm the request comes from a genuine app on a real device. This produces a cryptographic key and counter — no personal data.
• Technical data. Your IP address and basic request logs are processed transiently for security and rate limiting. Our website records aggregate, non-identifying visit counts by referral source.

How we use your information

• Provide the daily puzzle, AI scoring, history, and streaks.
• Manage your subscription and entitlements.
• Prevent abuse, fraud, and excessive automated requests.
• Maintain and improve the service.

AI scoring and service providers

To score your answers, the text you submit is sent to a third-party AI model through our backend. We share only what is needed to provide the service, and we do not use your submissions to advertise to you. Our service providers include:

• Apple — Sign in with Apple, In-App Purchases, App Attest.
• Cloudflare — hosting, database, and image storage.
• AI model providers — Anthropic Claude models generate your feedback; requests may be routed through an intermediary API gateway.

Sharing

We do not sell your personal information and do not share it for advertising. We disclose data only to the service providers above, or where required by law.

Retention and your choices

• Delete your account. In the App, go to Profile → Delete Account. This permanently removes your server-side account and associated data.
• Local data. Your attempt history is stored on your device; deleting the App removes it.
• We retain data only as long as needed to provide the service or meet legal obligations.

Children

HanziDiff is not directed to children under 13 (or the minimum age in your region), and we do not knowingly collect their personal information.

Security & international processing

Data is processed on Cloudflare’s global infrastructure and protected with industry-standard safeguards. No method of transmission or storage is completely secure, but we work to protect your information.

Changes

We may update this policy from time to time. Material changes will be reflected by the “Last updated” date above.

Contact

Questions? Email support@hanzidiff.vip.