Privacy policy

Last updated September 2026. The short version: if you have not created an account, nothing you do here leaves your own browser. There are no trackers, no analytics, no advertising, and we do not sell anything about anybody.

Without an account

Most of CruxStudy works with no account at all, and in that mode we do not receive your answers, your scores, your study plan or your name. All of it is written to your browser's own storage on your own device, under these keys:

• cruxstudy-state, your progress, scores, plan and settings
• cruxstudy-theme, which color theme you picked
• cruxstudy-win-*, where you left the calculator and scratch pad on screen

Clearing your browser data deletes all of it permanently, including from us, because we never had a copy. That is also the catch: it does not follow you to another device, and if you clear your history it is gone. That is what a membership account fixes.

We set no cookies and load no third-party scripts. The one external request the site makes is to Google Fonts for the typeface, which means Google receives your IP address the way it does on any site using their fonts. Nothing else on the page phones anywhere.

With a membership account

When you create an account we hold only what the product needs to work:

• Your email address and a display name
• Which account you belong to and your role: student, parent or educator
• The student's practice progress, scores and study plan, so they sync across devices
• Billing status, so we know whether the subscription is active

We use these processors and nothing else:

• Supabase for sign-in and the database
• Stripe for payment. Card details go straight to Stripe. We never see or store a card number.
• Resend for account email, such as an invitation or a weekly progress summary

We do not sell or rent personal information, we do not run advertising, and we do not share your data with anyone beyond the processors above.

Students, parents and educators

CruxStudy is used by high school students, most of them minors, and the account model is deliberately transparent about who can see what.

• A parent on the account can see that student's practice activity, scores and progress. That is the point of the parent dashboard, and the student should know it exists.
• An educator, if one has been invited, sees the same view and nothing about billing.
• A student sees only their own work. They cannot see a sibling's.
• We collect no more from a student than an email address and a display name.

CruxStudy is not intended for children under 13, and we ask that an account for a student under 13 be created and managed by a parent or guardian. If you believe a child under 13 has given us information directly, email us and we will delete it.

Deleting your data

Without an account, clear your browser data, or use "Clear everything on this computer" in the app. With an account, email hello@cruxsci.com and we will delete the account and its data. Cancelling a subscription on its own does not delete anything, deliberately, so that resubscribing restores your history.

Changes

If this policy changes in a way that affects what we collect or who sees it, we will say so on this page and, for account holders, by email. We will not quietly start collecting something new.

Contact

Questions, corrections or a deletion request: hello@cruxsci.com.