What we store, where, and what leaves your device.
The honest version: very little. No analytics, no advertising trackers, no third-party scripts, no cookies. The site is a static collection of HTML pages plus a small handful of browser-side JavaScript modules. Most of what could be considered “your data” never leaves your device.
What Euclid Lab does not collect
No analytics. No advertising or social-media trackers. No cookies. No fingerprinting. No third-party JavaScript on any page. No newsletter sign-up forms. No accounts.
The decision is deliberate: the project's doctrine is built around slowness, attention, and intellectual autonomy. Instrumenting the reader contradicts the spirit of that.
What lives in your browser
The site uses your browser's storage to remember settings and
practice progress between visits. Each item below is stored only on
the device where you create it, and is cleared if you clear your
browser's site data for euclidlab.net.
-
euclid.tutor.key.v1— your Anthropic API key, only if you choose to configure one for the AI tutor. By default it is held insessionStorageand disappears when you close the tab. If you tick “Remember on this device”, it moves tolocalStorageand persists until you click Forget or clear your browser data. Treat this storage as XSS-reachable; use only on devices you control. -
euclid.tutor.v1— per-case state for the tutor's diagnosis exercises (which case you have attempted, the verdict). No prose; just status and timestamps. -
euclid.practice.v1— your practice queue: text of each reconstruction attempt, the spaced-retrieval interval, a rough overlap score against your prior attempt. Your prose stays on your device. -
euclid.tweaks.v1— your theme, accent, and density preferences for the site's appearance. - Local backup. The Backup page exports the items above (excluding the API key) into a JSON file you can download and re-import later. The file stays on your device — nothing is uploaded.
What does leave your device
Two outbound destinations, and only when you take an action that requires them.
-
Anthropic. When you submit a diagnosis on the
Tutor page with an API key configured, the page sends your key,
the case data, and your diagnostic prose directly from your
browser to
api.anthropic.com. The site has no intermediary; we do not see this traffic. Anthropic's handling of the request is governed by their own privacy policy. If no key is configured, no request is made and the page tells you so. The full text of every prompt the AI receives is published at tutor-prompts — no hidden system messages. -
Web fonts. The site loads Spectral and JetBrains
Mono from Google Fonts (
fonts.googleapis.comandfonts.gstatic.com). This is a typical font-CDN request and reveals your IP address to Google for the request itself; no cookies or identifiers are set.
Hosting and request logs
The site is published via GitLab Pages and served through GitLab's CDN (which sits behind Cloudflare at the edge). Standard request logs may be retained by GitLab and Cloudflare for operational and security purposes; we do not access or analyse them. We have no server of our own.
If you write to us
Any email you send to the contact address remains in our inbox. We do not run mailing lists, do not subscribe you to anything, and do not share your address with anyone.
Children
The project is not directed at children under thirteen.
Changes
If this page changes materially, the date below changes too. The page itself is versioned in the public repository, so the full history of revisions is available there.
Last updated: 2026-05-09. Source on GitLab.