Cookie & Local Storage Notice

1.The short version

MatWorld sets cookies for one reason: to keep you signed in. Everything else we remember about your visit — your theme, your comparison set, an unfinished calibration — lives in your browser’s local storage and is never sent to us. Page-view analytics are cookieless. There is no advertising, no cross-site tracking, and no third-party marketing tag on the site.

That is why you see no cookie banner. Consent banners exist for cookies that need consent; we don’t use any. A test in our build fails if anyone adds a technology that would change this, so if it ever does change, this page will change first.

2.Cookies

All cookies are first-party and set by Clerk, the authentication service that handles sign-in. Blocking them means you cannot stay signed in; anonymous browsing works without them.

Name	Set by	Purpose	Type	Lifetime	Sent to
__session	Clerk (authentication)	Your signed-in session token. Without it nothing account-related works.	Strictly necessary	Short-lived; refreshed while you use the site, removed on sign-out	matworld.ai and clerk.matworld.ai
__client_uat	Clerk (authentication)	Records when your sign-in state last changed so pages can render the right signed-in / signed-out view immediately.	Strictly necessary	Up to 1 year	matworld.ai and clerk.matworld.ai
__clerk_db_jwt	Clerk (authentication) — development builds only	Development-instance session bridge. Never set on matworld.ai.	Strictly necessary	Session	Clerk development instance

3.Local storage

These keys persist between visits on this browser only. None is transmitted to our servers or anyone else; where a key influences a request we make (for example the compare set), the note says so.

Name	Set by	Purpose	Type	Lifetime	Sent to
theme	MatWorld (next-themes)	Your light / dark / system theme choice.	Functional	Until cleared	Nowhere
matworld:sidebar-collapsed	MatWorld	Whether you collapsed the navigation sidebar.	Functional	Until cleared	Nowhere
matworld:recent-views	MatWorld	The last 12 materials you opened, for the dashboard's recent list.	Functional	Until cleared	Nowhere
matworld:compare	MatWorld	The materials in your comparison set.	Functional	Until cleared	Nowhere (the compare page requests the listed materials from our API when you open it)
matworld:overlay	MatWorld	The curves in your overlay tray — which material and which curve — plus its axis settings. Curve points are not stored.	Functional	Until cleared	Nowhere (the overlay requests the listed materials from our API when you open it)
matworld:clipboard	MatWorld	The materials on your clipboard.	Functional	Until cleared	Nowhere
matworld:clipboard:pos	MatWorld	Where you dragged the clipboard bar.	Functional	Until cleared	Nowhere
matworld:clipboard:collapsed	MatWorld	Whether the clipboard bar is collapsed.	Functional	Until cleared	Nowhere
matworld:calibration-draft	MatWorld	Your in-progress calibration workbench: the parsed curves you uploaded, unit and condition choices, and fit options. This is the ONLY copy — the server does not store uploads.	Functional	Until cleared or until the draft format changes	Our API only when you click Fit or download a deck, and only for that request
mw:export:advanced:draft	MatWorld	Your Advanced Mode export selections, so a half-built card survives a reload.	Functional	Until cleared	Nowhere

4.Session storage

Cleared automatically when you close the tab.

Name	Set by	Purpose	Type	Lifetime	Sent to
matworld:user_tier	MatWorld	A cache of your plan (free / pro) so Pro features don't flash a lock while the page loads.	Functional	Tab session	Nowhere
matworld-selector-state	MatWorld	Axis and filter state of the Material Selector plot.	Functional	Tab session	Nowhere
matworld:materials:lastUrl	MatWorld	The last browser URL you were on, so 'back to results' keeps your filters.	Functional	Tab session	Nowhere
matworld:materials:lastClicked	MatWorld	Which result you clicked, to scroll it back into view when you return.	Functional	Tab session	Nowhere

5.Services that set no cookies

Vercel Web Analytics. Page views. Vercel derives a visitor hash from IP address and user agent with a daily-rotating salt; the IP is not stored and no identifier persists in your browser.
Sentry (error monitoring). If the page hits an error, the error, browser details, and a masked replay of the screen around the error are sent so we can fix it. Text is masked and media blocked by default. Nothing is sent when there is no error, apart from lightweight performance timings on a sample of page loads.

6.Pages you may be sent to

These providers operate pages you may be taken to. They set their own cookies under their own policies. We do not embed their scripts on matworld.ai.

Stripe Checkout and the Stripe billing portal. When you upgrade or manage a subscription. Card details are entered on stripe.com, never on matworld.ai.
Clerk Account Portal. Some account-management screens (password, connected accounts) are served by Clerk.

7.How to clear or block

Every browser lets you view, delete, and block cookies and site data for a site; look for “Site settings” or “Privacy” in your browser’s preferences. Clearing site data for matworld.ai signs you out and resets the preferences above; nothing on our side is affected. Blocking cookies for matworld.ai prevents sign-in but leaves anonymous browsing working.

8.Changes

The tables on this page are generated from the same inventory our code is tested against, so a new key or cookie cannot ship without appearing here. Material changes — in particular any technology that would require consent — are announced as described in the Privacy Policy.

Questions

MatWorld Inc., a California corporation

matworldai@gmail.com