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What we collect, why we collect it, and who we share it with — written for what the product actually does today.
Effective date: 23 May 2026
This privacy policy describes how Language Teacher (“we”, “us”, “our”) handles information when you use:
We aim to be specific and honest. We do not sell your personal information. We do not run third-party advertising or social tracking pixels on the Service today. If that changes, we will update this policy before enabling new trackers.
Account registration and sign-in. You can create an account with email and password, or sign in with Google via our authentication provider. When you register or use Google sign-in, we receive and store (through our backend) identifiers and profile fields needed to operate your account — typically your email address, account user ID, and basic profile information supplied by Google if you choose that option.
Learning preferences and profile data. If you use onboarding or study-target features, we store preferences such as which languages you study, onboarding answers, and study targets you set. Some of this may be mirrored in your browser’s local storage as a cache when you are signed in.
Quiz and learning activity. When you take quizzes or use learning tools while signed in, we store results and related data tied to your account — for example quiz sessions, individual answers where applicable, performance statistics (such as accuracy and attempt counts per character or item), custom study decks and deck items, and read-state for reading-stream excerpts. This data powers progress views, heatmaps, and recommendations inside the Service.
Contact and support messages. If you submit our Contact or Support form, we receive your name, email address, subject, and message. We use this only to respond to you and operate support.
Browser push notifications (optional). If you opt in to web push notifications, we store a push subscription object associated with your account (including an endpoint URL and cryptographic keys required to deliver notifications). You can revoke this in your browser or device settings.
Authentication cookies. When you sign in, our authentication provider sets session cookies so you stay logged in across pages and API requests. These are necessary for the Service to work for signed-in users.
Hosting and performance analytics. The Service is hosted on Vercel. We use Vercel Web Analytics, which collects privacy-oriented, aggregated usage data (such as page views and performance signals) to understand how the site is used. We do not use Google Analytics or similar ad-tech analytics on the Service at this time.
Server logs. Like most websites, our hosting infrastructure may log technical data such as IP address, request path, timestamp, browser type, and error information. We use these logs for security, debugging, and reliability.
Local storage in your browser. The Service stores some non-sensitive preferences locally, for example: sound volume settings, cached study targets, flashcard session state, quiz shortcut configuration, and draft text in certain tools. This data stays on your device unless a feature explicitly syncs it to your account in our database.
Cookie consent. We show a first-party cookie banner where you can accept all cookies, essential-only, or customize (analytics on/off). Your choice is stored in your browser (local storage) and, for audit purposes, logged in our database (visitor identifier, policy version, analytics yes/no, and account link if you are signed in). Optional analytics (Vercel Analytics) loads only if you allow analytics cookies. You can change your choice anytime on your Account page.
The optional Language Teacher — Kanji Heatmap Chrome extension highlights Japanese kanji on web pages other than https://languageteacher.io (the extension is disabled on our own site, where built-in heatmaps are used instead).
On-page processing. When you enable the heatmap, the extension scans visible text on the current page in your browser to find kanji characters and apply styling. That scanning happens locally in your browser. We do not upload full page text or your general browsing history to our servers.
Account-linked requests. To color kanji according to your progress, the extension calls our API on https://languageteacher.io using your existing sign-in session (cookies). Those requests may return aggregated statistics per kanji character (for example mastery band, accuracy percentage, and attempt count). The extension may cache this map locally for performance (for example about ten minutes).
Deck actions. If you use extension actions to open a character page or add kanji to a deck, the extension sends only the data needed for that action (such as the character and deck identifiers) to our API.
Extension storage. The extension uses Chrome’s storage permission for settings such as whether the heatmap is enabled and, during development, an optional API base URL. It does not request access to your Chrome browsing history as a separate permission.
Permissions. The extension requests broad host access so it can run on external sites where Japanese text appears. It explicitly excludes our own production domain (and local dev) from injection. For Chrome Web Store review, we describe this as on-page text processing for kanji highlighting only, not collection of a history feed.
We do not use your personal information for targeted advertising, and we do not sell it to data brokers.
We use a small set of infrastructure providers to run Language Teacher. They process data on our behalf only as needed to provide the Service:
Each provider has its own privacy policy and security practices. We choose providers appropriate for a learning application and configure access keys only on the server where possible.
What we do not use today: email marketing platforms, customer-data platforms, or social advertising pixels.
If you are in the European Economic Area or the United Kingdom, we rely on the following legal bases where applicable:
We retain account and learning data for as long as your account is active so you can continue your progress. If you delete your account or ask us to delete personal data, we will delete or anonymize identifiable information within a reasonable period, except where we must retain limited data for legal, security, or backup obligations.
Server logs and analytics aggregates may be kept for shorter rolling periods defined by our hosting providers.
We use industry-standard measures including HTTPS, authenticated API routes, database access policies, and secrets stored in environment variables rather than in public code. No online service can guarantee perfect security; please use a strong, unique password and keep your sign-in session private on shared devices.
The Service is not directed at children under 13 (or the minimum age in your country). We do not knowingly collect personal information from children. If you believe a child has provided us personal data, contact us and we will delete it.
Our providers may process data in the United States, the European Union, or other countries where they operate data centers. When data leaves your country, it may be protected by the provider’s contractual safeguards (such as standard contractual clauses) where applicable.
Depending on where you live, you may have the right to:
To exercise these rights, email us at contact@languageteacher.io. We may need to verify your identity before fulfilling a request.
You can also sign out at any time, clear site data in your browser, uninstall the Chrome extension, and disable notifications in browser settings.
We may update this policy when we ship new features (for example new integrations or payment). We will post the revised version on this page and update the effective date. Material changes may also be highlighted in the app or by email where appropriate.
Questions about privacy or this policy: contact@languageteacher.io, or use our Contact / Support pages.
For terms of use, see our Terms & Conditions.
Questions? See our Support page or Contact.