Mainichi Privacy Policy

Effective October 22, 2026

Mainichi is an iOS app for learning Japanese. It is operated by Timothy Horng, an individual in Arizona, USA ("Mainichi," "we," "us"). This policy explains what we collect, how we use it, who helps us run the app, and the choices you have. If you have questions, email timothyhorng@gmail.com.

Information we collect

Account information. To create an account you sign in with your email address (we send a one-time code; we never see a password), Sign in with Apple, or Google Sign-In. We receive your email address and an account identifier from the sign-in method you choose. If you use Sign in with Apple's "Hide My Email," we receive Apple's relay address instead.

Learning information you provide. Your Japanese level, lesson length and study preferences, the interests you choose, onboarding and placement answers, your answers to lesson questions, messages you send to Help, ratings and comments you send as feedback, and words you save. Mainichi does not ask for access to your camera or photo library.

Learning content created for you. Lessons, explanations, grades, recaps and notes that Mainichi generates for your account.

Lesson photos. Some lessons show photos chosen from Wikimedia Commons under open licenses. These are public images, not information about you, and their credits appear with the lesson.

Usage analytics. While you are signed in, the app records a small set of events: onboarding completed, lesson started, lesson completed, lesson ended early, a question graded (with its outcome), Help requested, and a step rated up or down. Each event can include simple counts such as a lesson's number of steps. Events are tied to a random analytics ID created for your account on your device, along with the app version, iOS version and a session ID. Analytics never include lesson text, your answers, Help messages, photos, your name, your email address, your account ID, or your device's name. We configure our analytics provider not to store IP addresses.

Device and notification information. If you allow notifications, we store a push notification token and your notification preferences so we can send daily lesson and weekly recap reminders. We use your time zone and study days to schedule lessons.

Diagnostics. The app keeps a limited technical log on your device, and our servers record technical details such as request timing and error codes so we can fix problems. These records use random identifiers and do not include your lesson content.

How we use information

We use this information to:

  • provide Mainichi: sign you in, build and grade personalized lessons, answer Help questions, and keep your progress in sync across devices;
  • send the notifications you turn on;
  • understand, in aggregate, how lessons are used so we can improve them;
  • respond to your feedback and requests;
  • keep the service secure and prevent abuse; and
  • meet legal obligations.

We do not sell your personal information, we do not share it for targeted advertising, we do not show ads, and we do not track you across other companies' apps or websites.

AI processing

Mainichi uses OpenAI's API to generate lessons and explanations, grade answers, and respond to Help messages. To do this, the relevant text is sent to OpenAI. We ask OpenAI not to store these requests for later retrieval. Under OpenAI's API policies, API data is not used to train its models, and OpenAI may keep it for up to 30 days to detect abuse. AI-generated content can be inaccurate; see our Terms of Service.

Who we share information with

We share information only with service providers that help us run Mainichi, only for that purpose, and we choose providers that commit to protecting it at least as well as this policy does:

  • Supabase: hosting, database, sign-in and file storage for your account and learning data.
  • OpenAI: AI generation, grading and image analysis, as described above.
  • PostHog: product analytics, hosted in the United States.
  • Apple: Sign in with Apple, push notifications, and app distribution.
  • Google: Google Sign-In, if you choose it.

We may also disclose information if required by law, to protect the rights and safety of our users or others, or as part of a transfer of the app to a new owner, who would remain bound by this policy.

How long we keep information

We keep your account and learning information while your account is active. When you delete your account, we delete your account, your learning data and your sign-in identity, and revoke Sign in with Apple access where possible. We keep only a minimal record that a deletion happened, which does not identify you. Copies in routine backups expire on their normal schedule. Analytics events are kept by our analytics provider for its standard retention period, and we will delete yours on request. AI provider retention is described above.

Your choices and rights

  • Delete your account: in the app, go to Settings, then Account, then Delete account.
  • Get a copy of your data: in the app, go to Settings, then Account, then Export my data. You will get a JSON file you can save or share.
  • Correct your data or delete analytics data: email timothyhorng@gmail.com. We will respond within 30 days.
  • Notifications and camera: you can turn these off at any time in the app or in iOS Settings.
  • Signing out stops analytics from your device.

Depending on where you live, including California and other US states, you may have rights to know, access, correct and delete your personal information, and to not be discriminated against for using them. We do not sell or share personal information as those laws define it. To use any of these rights, email us. We may need to confirm the request comes from you.

Children

Mainichi is not directed to children under 13, and we do not knowingly collect personal information from them. If you believe a child under 13 has given us information, email us and we will delete it.

Where information is processed

We and our service providers process information in the United States and other countries where those providers operate. By using Mainichi, you understand your information may be processed outside your country.

Security

We use encryption in transit, access controls and limited data collection to protect your information. No system is perfectly secure, so we cannot guarantee absolute security.

Changes to this policy

If we change this policy, we will update the effective date above. If a change is significant, we will also tell you in the app before it takes effect.

Contact

Timothy Horng · Arizona, USA · timothyhorng@gmail.com