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Terms of Service

Mastery — Adaptive Vocabulary Mastery System
Effective Date: February 23, 2026

1. Acceptance of Terms

By accessing or using the Mastery mobile application, web application, Chrome browser extension, or any related services (collectively, the "Service"), you agree to be bound by these Terms of Service ("Terms"). If you do not agree, do not use the Service.

These Terms constitute a legally binding agreement between you ("you," "your") and Valentin Seehausen, operating as a sole proprietor under the laws of Germany ("we," "us," "our").

2. Eligibility

You must be at least 16 years of age to use the Service. By using the Service, you represent and warrant that you meet this age requirement and have the legal capacity to enter into these Terms.

3. Account Registration

To use certain features of the Service, you must create an account using Google Sign-In, Apple Sign-In, or email/password registration. You are responsible for maintaining the confidentiality of your account credentials and for all activity that occurs under your account. You agree to notify us immediately at privacy@mastery-app.com of any unauthorized use.

We reserve the right to suspend or terminate accounts that violate these Terms.

4. Description of the Service

Mastery is an adaptive vocabulary mastery system designed for advanced English learners. The Service includes: vocabulary capture from browsing (Chrome extension), Kindle sync, and manual entry; a Memory Mirror vocabulary model that tracks and infers your vocabulary knowledge; spaced repetition practice sessions using the FSRS algorithm with multiple card types; vocabulary enrichment (definitions, translations, synonyms, audio, example sentences); and progress tracking across word stages.

The Service is provided "as is" and we continuously develop and improve it. Features may be added, modified, or removed over time.

5. Subscriptions and Payments

5.1 Free and Paid Tiers

The Service offers a free tier with limited features and a paid subscription ("Mastery Premium") with full access. The specific features available in each tier are described within the app and on our website.

5.2 Pricing

Subscription prices vary by region (purchasing power parity pricing) and by platform (web vs. mobile). Current prices are displayed at the point of purchase. All prices include applicable taxes unless stated otherwise.

5.3 Payment Processing

Web subscriptions are processed by Stripe. Mobile subscriptions are processed through the Apple App Store or Google Play Store via RevenueCat. By subscribing, you also agree to the payment terms of the applicable payment processor.

5.4 Renewal and Cancellation

Subscriptions renew automatically at the end of each billing period (monthly or annual) unless cancelled before the renewal date. You may cancel at any time through your account settings (web), the Apple App Store, or the Google Play Store. Cancellation takes effect at the end of the current billing period; you retain access until then.

5.5 Refunds

Refunds for web subscriptions are handled on a case-by-case basis; contact privacy@mastery-app.com. Refunds for mobile subscriptions are governed by the Apple App Store or Google Play Store refund policies.

5.6 Price Changes

We may change subscription prices with at least 30 days' advance notice. Continued use of the paid Service after a price change constitutes acceptance of the new price. If you do not agree, you may cancel before the new price takes effect.

6. User Content and Data

6.1 Your Data

You retain ownership of the personal data and learning data you provide to the Service (words, sentences, Kindle imports). By using the Service, you grant us a limited, non-exclusive license to process this data solely for the purpose of providing and improving the Service.

6.2 Data Portability

You may export your vocabulary data at any time through the app. Upon account deletion, we will delete your data in accordance with our Privacy Policy and Data Deletion Policy.

6.3 Prohibited Content

You agree not to submit content that is illegal, infringing, abusive, or harmful. We reserve the right to remove content that violates these Terms.

7. Acceptable Use

You agree not to:

  • Reverse-engineer, decompile, or disassemble the Service or any part thereof
  • Use automated scripts, bots, or scrapers to access the Service
  • Circumvent or disable security features, access controls, or usage limits
  • Resell, sublicense, or redistribute the Service or any content derived from it
  • Use the Service for any unlawful purpose or in violation of any applicable law
  • Interfere with or disrupt the Service or its infrastructure
  • Impersonate any person or entity or misrepresent your affiliation
  • Attempt to gain unauthorized access to other users' accounts or data

8. Intellectual Property

8.1 Our Rights

The Service, including its design, code, algorithms (Memory Mirror, adaptive card selection), enrichment content, user interface, and branding, is owned by us and protected by copyright, trademark, and other intellectual property laws. These Terms do not grant you any rights to our intellectual property except the limited license to use the Service.

8.2 Feedback

If you provide feedback, suggestions, or ideas about the Service, you grant us a non-exclusive, royalty-free, perpetual, irrevocable license to use, modify, and incorporate that feedback into the Service without obligation to you.

9. Third-Party Services

The Service integrates with third-party services including Kindle, Chrome, Supabase, Stripe, RevenueCat, Apple, and Google. Your use of these services is governed by their respective terms and privacy policies. We are not responsible for the practices of third-party services.

10. Disclaimer of Warranties

TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, THE SERVICE IS PROVIDED "AS IS" AND "AS AVAILABLE" WITHOUT WARRANTIES OF ANY KIND, WHETHER EXPRESS, IMPLIED, OR STATUTORY, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.

We do not warrant that the Service will be uninterrupted, error-free, or free of harmful components. We do not guarantee any specific learning outcomes.

Nothing in these Terms excludes or limits warranties that cannot be excluded or limited under applicable law, including consumer protection laws of the European Union.

11. Limitation of Liability

TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, OUR TOTAL LIABILITY ARISING OUT OF OR RELATING TO THESE TERMS OR THE SERVICE SHALL NOT EXCEED THE AMOUNT YOU PAID US IN THE 12 MONTHS PRECEDING THE EVENT GIVING RISE TO LIABILITY, OR €100, WHICHEVER IS GREATER.

WE SHALL NOT BE LIABLE FOR ANY INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL, OR PUNITIVE DAMAGES, INCLUDING LOSS OF DATA, LOSS OF PROFITS, OR BUSINESS INTERRUPTION.

These limitations apply to the fullest extent permitted by law. Nothing in these Terms limits liability for death or personal injury caused by negligence, fraud, or any liability that cannot be excluded under applicable law (including mandatory provisions of German civil law, BGB).

12. Indemnification

You agree to indemnify and hold us harmless from any claims, damages, losses, or expenses (including reasonable legal fees) arising from your use of the Service, your violation of these Terms, or your violation of any rights of a third party.

13. Termination

13.1 By You

You may terminate your account at any time by deleting your account through the app (Settings > Account > Delete Account) or by contacting privacy@mastery-app.com.

13.2 By Us

We may suspend or terminate your access to the Service at any time for violation of these Terms, with or without notice. In the event of termination for cause, you are not entitled to a refund of prepaid subscription fees. In the event of termination without cause, we will refund the pro-rata unused portion of any prepaid subscription.

13.3 Effect of Termination

Upon termination, your right to use the Service ceases immediately. We will delete your data in accordance with our Data Deletion Policy, subject to legal retention obligations.

14. Governing Law and Dispute Resolution

14.1 Governing Law

These Terms are governed by the laws of the Federal Republic of Germany, without regard to conflict of laws principles. If you are a consumer in the EU, you also benefit from mandatory consumer protection provisions of the law of your country of residence.

14.2 Jurisdiction

Any disputes arising from these Terms shall be subject to the exclusive jurisdiction of the courts in Germany. If you are a consumer in the EU, you may also bring proceedings in the courts of your country of residence.

14.3 EU Online Dispute Resolution

If you are a consumer in the EU, you may use the European Commission's Online Dispute Resolution platform at https://ec.europa.eu/consumers/odr.

15. Changes to These Terms

We may update these Terms from time to time. We will notify you of material changes at least 30 days in advance through the app or by email. If you do not agree to the updated Terms, you may terminate your account before they take effect. Continued use of the Service after the effective date constitutes acceptance.

16. Severability

If any provision of these Terms is found to be invalid or unenforceable, the remaining provisions will continue in full force and effect. The invalid provision will be modified to the minimum extent necessary to make it valid and enforceable.

17. Entire Agreement

These Terms, together with our Privacy Policy, EULA, and Data Deletion Policy, constitute the entire agreement between you and us regarding the Service and supersede all prior agreements and understandings.

18. Contact Us

If you have questions about these Terms, contact us at:

Valentin Seehausen
Email: privacy@mastery-app.com