Last updated 25 July 2026
X-Marks is a family app for making and playing real-world GPS treasure hunts. It is built so that we collect nothing: there are no accounts, no analytics, no advertising, and no app servers.
When you share a hunt, the entire hunt travels inside the link or file itself — there is no server holding it. Before it leaves your phone, the hunt is compressed and encrypted (AES-256-GCM, with the key derived inside the app using a hash-key scheme), so the messaging service carrying it, link-preview servers, and anyone who intercepts the message see only unreadable ciphertext. Only the X-Marks app can decrypt it. Because the key ships inside the app, this protects hunts in transit between copies of the app; treat hunt links like the family messages they travel in.
You choose who to send hunts to, using your own messaging apps (iMessage, WhatsApp, etc.). Those services handle the message under their own privacy policies.
Which treasures a hunter has found stays on that hunter's phone, full stop. The person who made a hunt is never told who found what, or when, and there is no server, link or sync that could carry it — because a hunt's points are real places, and "found point 3 at 2:41pm" would be a record of where a child had been. The app is built so that record never exists.
This site is a static page hosted on GitHub Pages. It exists to describe the app and to catch hunt links opened on phones without the app installed. It runs no analytics and sets no cookies. The encrypted hunt code in a link stays in your browser — this site never reads, stores, or transmits it. GitHub may keep standard web-server logs (such as IP addresses) as described in GitHub's privacy statement.
X-Marks is made for families. Because the app collects and transmits no personal data, there is nothing gathered about children (or anyone else).
Because a hunt points at real places, who may send one to a child is treated as a safety question rather than a convenience. Each phone is set up as either a grown-up's or a young hunter's. A hunter's phone cannot create hunts, and it will only open a hunt from someone already in its crew — anything else is refused outright, with no way to accept it, so knowing a child's phone number achieves nothing. Adding a trusted grown-up to that crew requires the passcode chosen when the phone was set up.
If the app ever changes how it handles data, this page will be updated before that version ships.
Questions? Email paulrobinson010@gmail.com.