Twain privacy policy
Last updated: 29 October 2026.
Twain is a Chrome extension for learning languages from YouTube videos. It has no account, no servers and no analytics. This page says what it handles, where, and why.
What Twain handles, all on your computer
| Data | Why | Where it stays |
|---|---|---|
| The captions of the video you're watching | To show them, translate them and look words up | In the page while you watch; translations are cached (see below) |
| Translations of caption lines and words | So a line is translated once, not every time | The extension's own storage (IndexedDB) on your computer |
| Words and lines you save, with the line, its translation, the video's ID and title, and the time | Your list, for review and export | The extension's own storage on your computer, until you delete them |
| Settings (languages, shortcuts, look) | To remember your choices | The extension's own storage on your computer |
| Subtitle timing per video | To keep a timing you set | The extension's own storage, for the last 300 videos |
| Dictionaries for the languages you watch | Base forms and meanings of words | The extension's own storage, until you remove them |
Twain never sends any of this to the developer or to anyone else. There is no tracking, no advertising and no selling of data.
Network requests
- YouTube. On
www.youtube.comonly, Twain reads the caption tracks YouTube's player lists and the captions the player loads. To show a second track of the same video (the original language, or human captions in your language), Twain requests it from YouTube the way the player does, with the same token the player uses. That token is used only in the page and is never stored. - Chrome's translator. Translation uses Chrome's built-in Translator. The first time a language pair is used, Chrome downloads a language pack after you click to start it. Translation then runs on your computer; text is not sent to a translation service by Twain.
- Dictionaries. The first time you watch a video in a language Twain has a dictionary for, Twain downloads that language's dictionary file once, in the background, from
twain-data.pages.dev(static files on Cloudflare Pages). The request contains nothing about you or the video; like any download, the host sees your IP address and which language's file is fetched. The dictionary is kept in the extension's storage; you can remove it in Settings. - Links you click. "Look it up in Wiktionary" and the video links in your saved list open those sites in a new tab, only when you click them.
The compatibility check
The optional compatibility check (Settings → "Run the compatibility check") records, in the extension's storage, technical facts about the caption requests on videos you play: parameter names, the token's length (never the token), response formats and sizes, and video IDs and titles. Its report, which you copy or save yourself, has video IDs but never titles. "Keep caption samples" is off by default; when on, it keeps the text of up to 8 caption files for use as test data. "Clear the list" removes it all.
Permissions
storage,unlimitedStorage: to keep your saved words, settings and the translation cache without a size limit cutting them off.sidePanel: Twain's panel for the transcript, saved words and settings.- Access to
https://www.youtube.com/*only: to show subtitles on YouTube's player.
Deleting your data
Delete saved items in the side panel's Saved tab. Removing the extension deletes everything it stored.
Credits
Dictionary data comes from Wiktionary (en.wiktionary.org), extracted with wiktextract (kaikki.org), and is available under the Creative Commons Attribution-ShareAlike licence.
Contact
Questions about privacy: open an issue on the project's repository, or use the contact address on the Chrome Web Store listing.