The rules, in plain words.

The short version

Learn, play fair, and do not copy the question bank. The daily practice is free. Pro is a subscription through Apple that renews until you cancel it. The app teaches system design as well as we can make it, and it does not promise you a job.

Agreeing to this

System Design Duel is made by BrayLabs LLC, an Oregon limited liability company. Using the app means you accept these terms. If you do not, the app is free to delete and we part on good terms.

You need to be 16 or older to use the app, and old enough where you live to agree to terms like these.

The date at the top is when this version took effect. Using the app after it means you accept this version.

Your account

The app creates an anonymous account for you when you first open it. That account lives on your phone. Until you sign in with Apple, losing the phone or deleting the app loses the account and its progress, and we cannot bring it back.

Your username is public. Do not impersonate anyone, and do not use a name that is hateful or obscene. We may change a username that breaks this rule, or one that belongs to somebody else's brand.

You can delete your account at any time from the You tab. The privacy policy says exactly what that erases.

Playing fair

A duel is a contest between two people, and the ladder only means something if it is played straight. So:

• Answer for yourself. No scripts, bots or tools that answer for you.
• One player per account, and no second accounts to move your own rating.
• Do not arrange results with an opponent.
• Do not collect, publish or pass around duel questions or their answers.
• Do not interfere with the app, its servers or other players' matches.

If we find that an account has broken these rules we may void its matches, reset its rating, remove it from the leaderboard, or close it. When nobody is available to play, a computer opponent takes the match. It plays to a fixed strength and does not appear on the leaderboard.

The questions

The questions, explanations, practice sets, case studies and design boards are ours. You may use them to learn. You may not copy the bank, scrape it, republish it, or use it to train or build another product.

Every question is written from a published source and links to it. Those sources belong to their authors. Naming a company or a product in a question does not mean it endorses the app or has any connection to it.

We check questions against their sources and review them, and we still get things wrong. Systems change, and so does what counts as good practice. If you think a question is mistaken, report it from the question itself and a person will look. Do not rely on the app as the only basis for a decision about a real system.

Videos

Some explanations come with a segment of a video from YouTube, played in YouTube's own player through YouTube API Services. The videos belong to their creators, and choosing one does not mean its creator endorses the app. By using the app you agree to be bound by YouTube's Terms of Service when you watch them. Videos are never part of what Pro pays for.

What you send us

Feedback on a question, a report, or a topic you ask for is yours, and by sending it you let us use it to improve the app without owing you anything for it.

Pro

The daily practice, every explanation, your streak, duels and the leaderboard are free and stay free. Pro is an optional subscription that adds more: the paywall in the app lists exactly what, and the price, before you buy.

• Payment is taken by Apple, through your Apple account, when you confirm the purchase.
• A subscription renews automatically for the same period, at the price shown, unless you cancel at least 24 hours before the current period ends.
• If a free trial is offered, it turns into a paid subscription when it ends unless you cancel before then.
• You manage and cancel a subscription in your Apple account settings. Deleting the app or your account does not cancel it.
• Refunds are handled by Apple, under Apple's own policy. We cannot issue one ourselves.

Pro belongs to the Apple account that bought it. Restore purchases on the You tab brings it back on a new phone. If we change a price, the change applies from your next renewal and Apple tells you first.

Changes to the app

We add, change and retire questions and features as the app grows. Ratings and ranks may be adjusted when the way they are worked out changes. We may stop offering the app. If we do, we will say so in the app beforehand.

What we do not promise

The app is provided as it is. We work to keep it accurate and running, and we do not guarantee that it always will be, or that using it will get you through an interview or into a job. To the extent the law allows, we are not liable for indirect or consequential losses that come from using the app, and our total liability to you is limited to what you paid us in the twelve months before the claim. Nothing here removes rights the law gives you as a consumer that cannot be signed away.

Apple

These terms are between you and us, not Apple. Apple is not responsible for the app or its content, and has no obligation to maintain or support it. Your use of the app must also follow the App Store's own terms.

Which law applies

These terms are governed by the laws of the State of Oregon, United States, without regard to its conflict-of-laws rules, and any dispute goes to the state or federal courts sitting in Oregon. If you are a consumer somewhere with rules that say otherwise, those rules win and nothing here is trying to take them from you.

Changes to these terms

If these terms change, the date at the top changes with them, and a change that matters is announced in the app before it takes effect.

Contact

Questions about any of this go to support@systemdesignduel.com. A person reads every message.

By post: BrayLabs LLC, 5441 S Macadam Ave, Ste R, Portland, OR 97239.