Privacy policy

Applies to the Chinese Brain browser extension for Firefox and Chrome and to this website. Last updated November 15, 2026.

Chinese Brain works without an account, and then everything stays in your browser: your word list, settings and API keys are stored locally and are never sent to the developer. There are no analytics, no ads and no tracking, and nothing is ever sold.

If you create an account

An account is optional. It keeps your word list in sync across your browsers. If you create one, our server (run on Cloudflare) stores:

• Your email address, to sign you in and to send a password-reset link when you ask for one. No other email is sent. With it: the day you created the account, the day you last used it, and how many items it holds.
• Your password, only as a salted hash. Nobody can read it, the developer included.
• Your synced data: the words you stamped (with their status, dates, and the sentences you met them in, which include the address and title of the page or video), sentences you saved, example sentences you hid or had Gemini write, and your settings. Your Gemini and Azure keys are never synced.

This data is used only to sync it back to you. It is not shared with anyone, except the companies that run the service for us: Cloudflare (hosting) and Resend (delivers the password-reset email, so it sees your email address).

On the account page you can download everything stored for you, change your password, or delete your account, which removes it and its data from the server right away.

What else leaves your browser

Some features send data to third-party services, only to perform the feature:

• Reading words and sentences aloud (default voice): the text is sent to Google's text-to-speech service (translate.google.com) when you press V or a play button.
• English subtitle line on YouTube: when YouTube does not provide an English translation, the video's Chinese caption lines are sent to Google Translate (translate.googleapis.com).
• Looking up a selection: when you select Chinese text and ask for its card and it is not a single dictionary word, the selected text is sent to Google Translate (translate.googleapis.com) for its English translation.
• Azure voice (optional, your own key): the text you play is sent to Microsoft Azure Speech in the region you choose.
• Gemini (optional, your own key): when you ask for subtitles, the YouTube video's link is sent to the Google Gemini API; when you ask for example sentences, the word and its short meaning are sent. On Google's free tier, Google may use these requests to improve its models.
• Image search: pressing I opens a DuckDuckGo image search for the word in a new tab.

The text of the pages you read is used only on your device to find words; it is not collected, sold or shared.

Deleting your data

Uninstalling the extension deletes what it stored in your browser. Deleting your account (on the account page) deletes what is stored on the server. You can also export or clear your word list from the extension's word-list page.

Contact

Cristian Bagrin · chris@cristianbagrin.com