Last updated: October 18, 2026
Initial version. It may change after a legal review; if anything important changes, we will let you know.
Cuby (gocuby.com) is a service to practice system design: you solve cases on a canvas, answer the interviewer's questions and get graded and, depending on your plan, AI feedback. It is offered by Cuby (gocuby.com).
By using Cuby you accept these terms. If you do not agree, do not use it.
You sign in with a link we email you, or with Google or GitHub. You are responsible for what is done from your account and for keeping access to your email.
You can start without an account: what you practice is tied to this browser and moves to your account when you sign in.
Free includes the daily challenge, one hint per challenge and one trial of AI feedback. Pro adds the whole catalog, every hint and AI feedback on each submission.
Prices and what each plan includes are on the Pro page. We may change them; if they change, we tell you beforehand.
Payments are processed by Polar (polar.sh), which acts as the Merchant of Record: it charges you, issues the invoice, applies any taxes and handles refunds under its policy. Cuby never sees or stores your card details.
Pro is a subscription that renews automatically. You can cancel it any time from Polar's portal; you keep Pro until the end of the period you paid for.
Do not use Cuby to harm the service or other people: no automated submissions, no flooding the service, no accessing other people's accounts and no bulk copying of the content to publish or sell it.
Your diagrams and answers are yours. You allow us to store and process them to provide the service, including AI feedback.
Cuby's cases, texts, grading and design belong to Cuby. AWS, Google Cloud and Azure names and icons belong to their owners; Cuby is not affiliated with them.
AI feedback is generated by a language model. It is guidance, it can be wrong, and it does not replace the judgment of an experienced person.
We do our best to keep Cuby running, but we do not guarantee it will be free of outages or errors. We may change or discontinue features.
Cuby is provided as is. To the extent the law allows, we are not liable for indirect damages arising from its use.
You can ask us to delete your account by writing to hola@gocuby.com. We may suspend an account that does not follow these terms.
If we change these terms in an important way, we tell you by email or in the app before they apply.
Write to us at hola@gocuby.com.