This Privacy Policy explains what information Stack Check ("we," "us," "the app") collects, how it's used, and what choices you have. Stack Check is an unofficial Magic: The Gathering companion tool — rules search, card lookups, Commander Bracket/Game Changer reference, AI-assisted deck analysis ("Rule 0"), and an AI-assisted rules Q&A ("Ask a Judge").
If you use Stack Check without an account, your favorited rules, saved Rule 0 decks, and Ask a Judge history are stored only in your browser's local storage — we never see this data, and it stays on that specific device/browser. Creating an account and choosing to sync moves relevant parts of this into our database (see below) so it follows you across devices.
If you subscribe to a paid tier, payment is handled entirely by Stripe, our payment processor. We do not receive or store your full card number — we retain only a Stripe-issued customer/subscription reference so we know which tier you're on.
We do not sell your personal information, and we do not use it for advertising.
Stack Check is built on top of several third-party services, each of which processes certain data as part of making the app work:
| Service | What it receives | Why |
|---|---|---|
| Anthropic (Claude) | Card photos (Scan a Card), decklist text (Rule 0), your questions and any card text you provide (Ask a Judge) | Powers the app's AI-assisted features |
| Scryfall | Card names | Public card data lookups — no personal information sent |
| Supabase | Account credentials, saved decks, favorites, subscription status | Hosts our database and authentication |
| Stripe | Payment and billing information | Processes subscription payments |
| Vercel | Standard request/server logs | Hosts the application and backend |
Each of these providers has its own privacy policy governing how it handles data; we encourage you to review theirs if you want the full picture beyond what we've summarized here.
Account data is stored in a hosted Supabase database with access controls (row-level security) that scope each account's data to that account alone — no user can read another user's saved decks, favorites, or account details through the app itself. Passwords are hashed and managed entirely by Supabase's authentication system; we never see them in plain text.
No system is perfectly secure, and we can't guarantee absolute security, but we take reasonable, standard precautions appropriate for a project of this size.
If you have a privacy-specific question or request that isn't covered by the self-service options above, you can reach us at mtgstackcheck@gmail.com.
Stack Check is not directed at children under 13, and we do not knowingly collect personal information from children under 13. If you believe a child has provided us with personal information, contact us and we'll delete it.
We use browser local storage (not tracking cookies) to remember your favorites, saved decks, and Ask a Judge history when you're not signed in, and to remember your session when you are. We don't use third-party advertising trackers.
We may update this policy as the app changes. Material changes will be reflected by updating the "Last updated" date above; continued use of the app after changes take effect means you accept the revised policy.
Questions about this policy: mtgstackcheck@gmail.com
For bugs or app issues, please use the "Report a problem" link in the app instead, so we can keep this inbox focused on account and privacy matters.