Terms of Use

Underhook · Effective September 2, 2026

These terms cover the Underhook app and this site. Using either means you accept them. They are written plainly on purpose.

What Underhook is

Underhook is a practice app for Brazilian Jiu-Jitsu: a guided path of scenario questions, theory, and sparring games you play on your phone between classes. It trains decisions. It is a study tool, not a coach and not a replacement for training with qualified instructors on a mat.

Training disclaimer

Jiu-jitsu is a contact sport and carries a real risk of injury. Nothing in the app is medical advice, and nothing in it is instruction to attempt a technique unsupervised. Techniques discussed in the app should only be practised in a supervised setting with a willing partner at a level appropriate to you. You train at your own risk, and you are responsible for your own safety and your training partners'.

Your account

You may start anonymously. Signing in with Google or with Apple links your progress to that identity so it survives a new phone.
One account is for one person. Keep your sign-in to yourself.
Underhook is not directed to children under 13, and accounts are not for them.
You can delete your account and its data at any time — in the app, or by request: how to delete your account.

Pro, and how it is billed

The belt path is free. Every lesson and every position is free, to the belt test. Pro lifts the daily stamina limit, unlocks Kat the rival, and adds a second streak freeze.
Pro is sold as a monthly or annual subscription, or as a one-time lifetime purchase. The price is shown on screen before you buy.
Payment is handled by the store, not by us — Google Play on Android, Apple on iPhone. Subscriptions renew automatically until cancelled, and you cancel or manage them in the store: Google Play → Payments and subscriptions, or Settings → your Apple Account → Subscriptions.
Refunds are the store's, under its own policy. We do not take or hold your payment details at any point.
The 3 days of Pro a new account receives is a gift from us, not a store trial: no card is attached, nothing converts, and nothing charges when it ends.
Deleting your account does not cancel a subscription. Cancel it in the store.

Content and use

The lessons, questions, artwork, characters and text in Underhook are ours, and you get a personal, non-transferable right to use them inside the app. Do not copy, resell, scrape or redistribute the content, and do not attempt to break, overload or reverse engineer the service. What you add — a display name, an avatar, an academy — stays yours; you give us only the permission needed to show it back to you inside the app.

The service changes

Underhook is under active development. Features arrive, change and occasionally leave. We may update these terms; the effective date above moves when we do, and continued use after that is acceptance. If a change materially reduces what you paid for, the store's refund policy is your remedy.

Availability and liability

The app is provided as it is, without a promise that it will be uninterrupted or error free. To the extent the law allows, we are not liable for indirect or consequential loss, and our total liability is limited to what you paid us in the twelve months before the claim.

Contact

Questions about these terms: hello@underhook.xyz