Overview
Musubu ("we", "our", "the Service") is a Japanese kanji learning tool. This policy explains what data we collect, how we use it, and your rights regarding that data.
Data We Collect
Account Information. When you register, we store your username and a securely hashed password. We do not collect your email address unless you provide one voluntarily.
Learning Data. We store data you create while using the Service, including:
- Word status markings (known, learning, bookmarked)
- Saved word graphs and their configurations
- Custom and AI-generated example sentences
Payment Information. If you subscribe to Premium, payment is processed entirely by Stripe. We do not store your credit card number, bank details, or other payment credentials. We store only your Stripe customer ID and subscription status to manage your plan.
Technical Data. Our servers may log IP addresses, request timestamps, and user-agent strings for security and abuse prevention. These logs are retained for a limited period and are not linked to your learning data.
How We Use Your Data
- Provide the Service — store your progress, generate graphs, and manage your account.
- AI Sentence Generation — when you request AI-generated sentences, we send the relevant word or kanji to OpenAI's API. We do not send your account information or personal data to OpenAI.
- Process Payments — manage your subscription status via Stripe.
- Improve the Service — understand usage patterns in aggregate to fix bugs and improve features.
Third-Party Services
We use the following third-party services:
- Stripe (privacy policy) — payment processing for Premium subscriptions.
- OpenAI (privacy policy) — AI-powered sentence generation. Only the requested word/kanji is sent; no personal data is shared.
We do not sell, rent, or share your personal data with any other third parties.
Cookies
We use a session cookie to keep you logged in. This cookie is essential for the Service to function and cannot be opted out of while using an account. We do not use analytics cookies or third-party tracking cookies.
Data Retention & Deletion
Your account and learning data are retained for as long as your account exists. You may request deletion of your account and all associated data at any time by contacting us. Upon deletion:
- Your account, learning data, graphs, and sentences are permanently removed.
- If you have an active Premium subscription, it will be canceled via Stripe.
- Server logs containing your IP address are automatically purged on a rolling basis.
Data Security
We use industry-standard practices to protect your data, including encrypted connections (HTTPS), securely hashed passwords, and limited access to production systems. However, no method of transmission or storage is 100% secure.
Children's Privacy
The Service is not directed at children under 13. We do not knowingly collect data from children under 13. If you believe a child has provided us with personal data, please contact us so we can delete it.
Changes to This Policy
We may update this policy from time to time. Changes will be reflected by the "Last updated" date at the top. Continued use of the Service after changes constitutes acceptance of the updated policy.
Contact
If you have questions about this privacy policy or wish to request data deletion, please contact us.