Terms of Service

These Terms of Service (“Terms”) govern your use of Tenkai (the “Service”) at https://tenkai.uk. By accessing or using the Service, you agree to these Terms. If you do not agree, please do not use the Service.

1. The Service

Tenkai is a free online study tool for learning English and Japanese vocabulary, kanji, grammar, and exam-style content. The Service is provided as-is, on a best-effort basis, by a personal-scale operator.

2. Eligibility and accounts

You must be at least 13 years old to create an account. By registering, you confirm you meet this requirement.

You are responsible for keeping your password secure and for activity that occurs under your account. We are not liable for losses caused by unauthorised account use; please notify us promptly if you suspect a compromise.

You may sign in via email + password or a supported single sign-on provider (Google, Apple, LINE). Each method is optional; the Service works with whichever you choose.

3. Acceptable use

You agree NOT to:

• Use the Service to harass, defame, or harm others.
• Submit content that is unlawful, hateful, sexually explicit, or designed to mislead other learners.
• Scrape, crawl, or programmatically extract Service content in bulk except via the documented /api/mobile/* endpoints with a valid bearer token, or within the rates declared in our robots.txt.
• Attempt to gain unauthorised access to other users' accounts or to Service infrastructure.
• Use the Service's content to train competing AI models or to build a competing dataset.
• Circumvent rate limits or other protective measures.

We may suspend or terminate your account if we reasonably believe you have violated these Terms.

4. User-submitted content

When you submit content to the Service — including custom sentences, notes, decks, definitions, flagged questions, ingested documents, OCR uploads, and tribunal feedback — you retain ownership of your submissions.

You grant Tenkai a worldwide, non-exclusive, royalty-free licence to host, store, display, and process your submissions for the purpose of operating the Service. This licence ends when you delete the submission or your account, except where retention is required by law or for backup integrity (up to 30 days after deletion).

Some submissions (e.g. tribunal sentence flags) are visible to other users by design. The Service moderates and may remove submissions that violate Section 3.

You can delete your submissions at any time via the in-Service tools (per-card edit, deck removal, account deletion).

5. Service content and intellectual property

All content displayed on the Service is copyrighted and proprietary to Tenkai unless explicitly stated otherwise. This includes the user interface, original editorial wordlists, grammar explanations, glossary entries, hand-authored exam questions, page layouts, and code.

Third-party content is used under licence or because it is open-source. Sources and licences are documented in docs/DATA_LICENSES.md, including but not limited to:

• Vocabulary & dictionaries: JMdict / JMnedict, KANJIDIC2, KanjiVG (CC-BY-SA, courtesy of the EDRDG).
• Learner wordlists: CEFR-J, Octanove C1/C2, NGSL, NAWL.
• Frequency data: wordfreq, SUBTLEX-US, Google 10000.
• Pitch accent: Kanjium (CC-BY-SA).
• Example sentences: Tatoeba (CC-BY).
• Public-domain literary works: Project Gutenberg (English PD) and Aozora Bunko (Japanese PD).

You may view content for personal study. You may NOT bulk-export, redistribute, or republish editorial content (hand-authored questions, glossary entries, exam banks) without explicit written permission. Reasonable personal-use export of YOUR OWN study data via /account or /settings is always allowed.

6. Third-party services

The Service integrates with Google, Apple, LINE, Resend, Vercel, Neon, and (optionally) Upstash, Google Cloud Vision, and Google Cloud TTS. Your use of those services is also governed by their own terms. See the Privacy Policy for the full list and links.

7. Disclaimer of warranty

THE SERVICE IS PROVIDED “AS IS” AND “AS AVAILABLE”. WE MAKE NO WARRANTIES, EXPRESS OR IMPLIED, AS TO MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. WHILE WE TAKE PAINS WITH GRAMMAR ACCURACY AND CONTENT CORRECTNESS, WE DO NOT WARRANT THAT YOUR USE OF THE SERVICE WILL RESULT IN ANY PARTICULAR LEARNING OUTCOME OR JLPT / CEFR EXAM SCORE.

8. Limitation of liability

TO THE MAXIMUM EXTENT PERMITTED BY LAW, TENKAI WILL NOT BE LIABLE FOR INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL, OR EXEMPLARY DAMAGES, OR FOR LOSS OF PROFITS, DATA, OR GOODWILL, EVEN IF ADVISED OF THE POSSIBILITY.

Our total liability for any claim arising out of these Terms or your use of the Service is limited to fifty pounds sterling (£50) — the Service is offered free of charge, so this cap reflects our actual exposure.

Nothing in these Terms excludes or limits liability that cannot lawfully be excluded or limited under English law, including liability for death or personal injury caused by negligence, or for fraud.

9. Termination

You may stop using the Service at any time and delete your account from /account.

We may suspend or terminate your access if you violate these Terms, if required by law, or if maintaining your account becomes operationally infeasible. We will give reasonable notice where possible.

10. Changes to these Terms

We may update these Terms. Material changes will be announced via an in-app notice for signed-in users. Continued use after the effective date of changes constitutes acceptance. If you do not accept the new Terms, your sole remedy is to stop using the Service and delete your account.

11. Governing law

These Terms are governed by the laws of England and Wales. You agree to the exclusive jurisdiction of the courts of England and Wales for any dispute arising out of these Terms.

12. Contact

Questions about these Terms: legal@tenkai.uk.