Terms of use
Katsuyokei · version 1.0 · last updated: 4 September 2026
What this app is
Katsuyokei is an educational app for practicing the conjugation of Japanese verbs and adjectives. It is not a service, a course, or advice — it runs entirely on your device and needs no account.
License
You get a personal, non-exclusive, non-transferable right to use the app on devices tied to your Apple Account, under the App Store terms. You may not resell the app, decompile it, or extract the study material from it in order to pass that material on.
In-app purchases
Premium is a one-time non-consumable purchase — no subscription, no automatic renewals. It opens levels 3 through 5, the full vocabulary pool, and practice on your weakest forms. Levels 1 and 2 stay free in their entirety.
Payments and refunds are handled solely by Apple, under the App Store terms. The purchase is tied to your Apple Account and can be restored on another device with “Restore purchases” in Settings.
Your data
Your study progress is stored on the device alone. We have no access to it and no way to recover it once you delete the app or erase your progress in Settings.
Accuracy of the material
Forms are derived from conjugation rules and covered by tests, but a natural language has exceptions and registers that no set of rules covers completely. This app does not replace a dictionary, a textbook, or a teacher. If you find a form that looks wrong, write in — reports like that come first.
Liability
The app is provided “as is”. To the extent permitted by law, the author is not liable for damages arising from its use, including the loss of study data. None of this limits consumer rights granted by mandatory provisions of law.
Changes to these terms
These terms may change as the app develops. Changes appear on this page along with the date of the update; continuing to use the app after they are published means accepting them.
Governing law
Polish law, subject to the mandatory consumer-protection provisions in force in your country of residence.