Duetbook Privacy Policy

Effective October 23, 2026

Duetbook is an audiobook and podcast player for people learning a language, made by Junichiro Horikawa (shown on the App Store as JUNICHIRO HORIKAWA). This policy covers the Duetbook apps for iPhone, iPad and Apple Watch, its widgets, the Duetbook menu bar app for Mac, and this website.

On your device

Duetbook keeps these on your device: the audiobooks, ebooks and podcast episodes you add; their transcripts and translations; the sentences and words you save, with their audio clips, translations, explanations and review history; bookmarks and notes; how long you listened each day; your settings.

Speech recognition (Apple’s, or Whisper once downloaded), translation (Apple’s, or the downloaded translation model), grammar explanations (Apple Intelligence, or the downloaded model) and voices (Apple’s, or the downloaded Japanese voice) all run on the device. Dictation answers are checked on the device and not kept; sentences you missed are saved for review.

The widgets and the Apple Watch app show the current book’s title, author, chapter, progress and cover, which they get from the iPhone app. The watch sends back only playback commands.

iCloud

If you are signed in to iCloud, a new library is kept in iCloud so your devices share it. Duetbook then uses:

• iCloud Drive, in the Duetbook folder: audio files, covers, transcripts, translations and saved audio clips.
• Your private iCloud database: the library’s records (books, chapters, folders, collections, tags, bookmarks and notes, saved sentences and words with their review schedule, followed podcasts, listening time per day).
• iCloud key-value storage: where you are in each book.
• iCloud Keychain: the username and password of a private podcast feed, if you add one.

This data is in your iCloud account, under Apple’s terms and privacy policy. We have no access to it.

If you use “Transcribe on My Mac”, the iPhone leaves a request in iCloud Drive (the book’s title, language and track names) and the Mac app transcribes the audio on the Mac.

When Duetbook goes online

• Apple’s podcast directory. Searching, browsing categories and top shows sends your search words, the language you chose and your device’s country or region to Apple (itunes.apple.com).
• Podcast publishers. Duetbook fetches feeds, artwork, episode audio and published transcripts straight from the publisher or its hosting company. As with any podcast app, those servers see your IP address and the app’s name, and publishers may count downloads. The feeds of shows you follow are checked when you open the app and in the background, and their newest episodes download automatically (three unless you change it in the show’s settings), on Wi-Fi unless you allow cellular data.
• Private feeds. A private feed’s username and password are sent only to that feed’s server.
• Apple’s downloads. Speech recognition and translation languages, and Duetbook’s optional downloads (Whisper, the Japanese voice, the translation model), come from Apple’s servers.
• A web address you enter. “Download from URL” fetches the file from that address and nowhere else.
• A translation server you set up. In Settings › Translation › Server you can connect a server that speaks the OpenAI chat API, such as LM Studio or Ollama on your own computer, or a cloud service. Duetbook uses it only after you enter its address and model. It then receives the sentences to translate or explain, the sentences around them, the book’s title and the two languages. That server’s operator handles them under its own terms; we don’t receive them. Its API key stays on this device and isn’t synced.

Purchases

Duetbook Pro is bought through the App Store. Apple handles the payment, and we receive no payment details and no information about your Apple Account. The app checks your purchase on the device.

Crash reports and messages to us

If you have chosen to share analytics with app developers (Settings › Privacy & Security › Analytics & Improvements), Apple may pass us crash reports and diagnostics that don’t identify you.

If you write to us through the support form, the form is run by Tally (tally.so), which receives what you enter, such as your email address and message, and passes it to us. We use it only to answer you and delete it once the conversation is over. Tally handles it under its privacy policy.

This website

This site has no analytics, cookies or ads, and loads nothing from other sites. Its fonts and recordings are served from the site itself. It is hosted on GitHub Pages; GitHub records the IP addresses of visitors for security, as its privacy statement describes.

Children

Duetbook collects no information from anyone, children included. Podcasts come from their publishers, and some are marked explicit.

Deleting your data

Deleting a book in Duetbook removes its audio, transcript and translations. Sentences and words you saved from it stay in Review until you delete them. Deleting the app removes everything kept on the device. To remove what is in iCloud, delete the Duetbook folder in Files › iCloud Drive, and Duetbook’s data in Settings › [your name] › iCloud › Manage Account Storage.

Changes

If this policy changes, the new version is posted at this address with a new date.

Contact

Write to us through the support page.