Terms of Service

By accessing or using JStacked ("the Service") at j-stacked.com, you agree to be bound by these Terms of Service. If you do not agree, do not use the Service.

JStacked is a Japanese language learning tracker that aggregates study data from third-party apps (WaniKani, BunPro, Renshuu, Anki) and provides readiness analytics, mock tests, and progress dashboards to help you prepare for the Japanese Language Proficiency Test (JLPT).

• You are responsible for maintaining the security of your account and any API keys you connect.
• You must provide a valid email address. One account per person.
• You must be at least 13 years old to use the Service.
• We reserve the right to suspend or terminate accounts that violate these terms.

You agree not to:

• Use the Service for any unlawful purpose
• Attempt to reverse-engineer, scrape, or extract data from the Service at scale
• Share your account with others or resell access to the Service
• Use automated tools to generate excessive API requests (see Section 5)
• Attempt to gain unauthorised access to other users' data
• Interfere with or disrupt the integrity or performance of the Service

The Service enforces rate limits to ensure fair access for all users:

• Mock tests: 30 requests per hour per user
• Analytics and sync: 60 requests per hour per user
• Data export: 10 requests per hour per user

Requests exceeding these limits will receive a 429 Too Many Requests response. Repeated or deliberate abuse of the API may result in account suspension.

All content, design, code, and branding on JStacked — including the Tsumi-kun mascot, dashboard layout, and analytics engine — is owned by JStacked and protected by copyright law. You may not copy, reproduce, or distribute any part of the Service without written permission.

JLPT vocabulary and kanji data used in mock tests is derived from publicly available sources. JStacked does not claim ownership of that underlying linguistic data.

JStacked connects to third-party services (WaniKani, BunPro, Renshuu, Anki) using API keys you provide. You are responsible for ensuring you have the right to use those keys and that your use complies with the respective third party's terms of service. JStacked is not affiliated with or endorsed by any of these services.

JStacked Premium is a paid subscription billed monthly or annually via Stripe. Subscriptions auto-renew unless cancelled before the renewal date. You can manage or cancel your subscription at any time from your account settings. Refunds are handled on a case-by-case basis — contact us within 7 days of a charge if you believe you were billed in error.

The Service is provided "as is" without warranties of any kind. We do not guarantee that the Service will be uninterrupted, error-free, or that readiness scores accurately predict JLPT exam outcomes. JLPT pass probability figures are estimates based on your study data and should not be relied upon as guarantees.

To the fullest extent permitted by law, JStacked shall not be liable for any indirect, incidental, or consequential damages arising from your use of the Service. Our total liability to you shall not exceed the amount you paid us in the 12 months preceding the claim.

We may update these terms from time to time. Continued use of the Service after changes constitutes acceptance. We will update the date at the top of this page when changes are made.

Questions about these terms? Email us at hello@j-stacked.com.