Privacy Policy

(a) Learning data (on-device)

• Words you've browsed, review history, wrong-answer log, study plan settings
• This data is stored locally in SQLite on your device.

(b) Sync and anonymous usage data (server-side, first-party)

• Visitor ID: an anonymous, randomly-generated UUID stored on your device. It is not linked to your name, email, Apple ID, Google account, or any other personal identifier.
• Word-view events: when you read or quiz a word, we record the word ID, timestamp, a source tag (learn / review / quiz), and your visitor ID. This is used to deduplicate views and measure engagement (DAU/WAU/MAU) so we can improve the app.
• Learning-progress sync: the IDs and timestamps of words you've browsed, the IDs of words you've marked for review, your wrong-answer log (word ID, wrong-answer count, first and most recent wrong-answer time), your study plan settings (daily new words, daily review count, total goal, mode), and your language preference. All of it is sent as word IDs, timestamps and setting values, so we keep a copy of your learning record on our server as well as on your device.
• Which option you pick in a quiz is not uploaded; we only record that a word was answered incorrectly, so it can be scheduled for review. Any text you enter is not uploaded.

(c) Connection information (observed server-side)

On top of the fields the app itself sends, the server records the following whenever your device connects:

• IP address: the network address your device connected from.
• Country / region code: a two-letter code derived from that IP address (for example TW, HK, JP), used to chart where our users are. We store it at country / region level only and make no finer-grained location inference.
• Last used: the most recent time you used the app.
• App version and platform: on every connection the app also sends its own version string (for example 1.0.4 (65)) and platform (iOS or Android), so we can see which build each device runs and on what platform. Device brand, model and operating system version are not uploaded (see (d) below).

(d) Technical info we collect automatically

The following is provided by the operating system and the app store platform (Apple App Store / Google Play) through their standard mechanisms. The app does not upload it separately, and it is used for bug triage:

• Device model, operating system version, app version
• Crash logs

In addition, from version 1.0.4 the app sends its own version string and platform (iOS / Android) with every API request, so we can see how each release is used and diagnose problems specific to a build. Device brand, model and operating system version are still not sent by the app.

• Learning data: on-device storage is the source of truth. A minimal copy is also synced to our server (see (b) above). The anonymous identifier used to recognise you lives in the device's encrypted storage — if it is removed along with the app, a reinstall is treated as a new learner and your previous progress does not come back automatically.

• Visitor ID + word-view events: used to deduplicate views and measure engagement so we can improve content quality and prioritize features.

• Learning-progress sync: lets us keep a copy of your learning record on our server.

• Connection information: used to count how many devices are using the app, chart which countries / regions our users are in, and see when each user last used it. It is not linked to a name, an email address, or any other identifying data, is not used for advertising or marketing, and is not shared with any third party.

• We do not track your study behavior for advertising or marketing.

• We do not share your visitor ID, word-view events, learning progress, or connection information with any third party.

• We do not sell your personal information to data brokers.

• We do not secretly read your contacts, photos, location, or other unrelated data.

• We do not require an account, login, or sign-up.

• We do not collect precise location, device identifiers for advertising (IDFA), or biometric data. We record only the IP address and the country / region code derived from it, and make no finer-grained location inference.

• We do not collect email addresses in v1.0.

The app does not embed any third-party SDKs for analytics, advertising, or attribution. All data collection described above is first-party (handled by our own backend at api-satvocabboost.coretrix-tech.com).

• Access / correct / delete: email support@coretrix-tech.com at any time. We will respond within 30 days. When you ask us to delete, we also delete the connection information linked to your visitor ID (IP address, country / region code, last-used time).

• Reset on-device data: open the app → Settings → Data & Privacy → Reset learning data.

• Uninstall: removes all on-device data and disconnects your visitor ID from future uploads.

The app is not directed at children under 13. We do not knowingly collect personal information from children under 13. If you believe we have inadvertently collected such information, please contact support@coretrix-tech.com and we will delete it within 7 days.

We use HTTPS / TLS for all network requests, industry-standard server hardening, and access controls to limit who can view stored records. Visitor IDs, word-view events, learning-progress sync data and connection information (IP address, country / region code, last-used time) are kept in our own infrastructure (Alibaba Cloud ECS) and are not transmitted to any third party.

We may update this policy from time to time. Updates will trigger an in-app notice and the "Last updated" date on this page will be refreshed. Material changes will be posted on this page.