Cookie notice
Version 1.0.0 · Last updated 29 July 2026
We would rather explain our cookies once, properly, than interrupt you with a banner. This page lists every cookie kyn brain sets and what each one is for, and lets you turn the optional ones off in one click.
All of them are first-party: they are set by brain.withkyn.com and readable only by us. We run no advertising cookies, no third-party trackers, and nothing that follows you across other sites. See our Privacy Policy for how we handle personal data more generally.
1. Your choice
Optional cookies are on by default. Turning them off applies to this browser: we stop setting them, remove the ones already set, and switch off product analytics for you. Nothing about the Service stops working, and you can change your mind here at any time.
Optional cookies are on. Turning them off takes effect immediately and removes the ones already set.
You can also clear or block cookies in your browser settings. If you block them entirely, sign-in will not work, because the session cookie is how we know it is you.
2. Cookies we need to run the Service
These are strictly necessary: without them you could not sign in, or we could not honour a choice you have made. They are not covered by the switch above.
| Cookie | What it does | How long |
|---|---|---|
| authjs.session-token | Keeps you signed in. Holds a random session id only, which we look up in our database; your name, email, and content are never in the cookie. | 30 days, or until you sign out |
| authjs.csrf-token | Protects the sign-in form against being submitted from another site on your behalf. | Until you close the browser |
| authjs.callback-url, authjs.pkce.code_verifier, authjs.state | Carry you safely through the Google sign-in round trip and back to the page you started from. | Minutes, cleared when sign-in finishes |
| kyn_optional_off | Set only if you turn optional cookies off below, so we remember your choice. It holds one character and nothing about you. | Up to 400 days, or until you turn optional cookies back on |
3. Optional cookies
These four help us understand how people find kyn brain, credit members who introduce a friend, and test which wording is clearer. None of them carries an advertising identifier, and none is shared with an ad platform.
| Cookie | What it does | How long |
|---|---|---|
| kyn_signup_source | Remembers which channel first brought you here, as a single word such as “search” or “share”. Never a web address, campaign text, or identifier. We read it once, to record the channel if you create an account. | 30 days |
| kyn_loop_surface | Remembers that you arrived on a shared takeaway or a circle invite, so we can tell how many accounts start that way rather than from our own pages. | 30 days |
| kyn_referral | Remembers the specific share or invite link you arrived on, so that if you create an account and later move to a paid plan, the member who introduced you can receive their referral credit. They only ever see anonymous counts. | 30 days |
| kyn_exp | Holds a random value, with no identifier or account information in it, so that when we are testing two versions of the wording on a public page you keep seeing the same one. | 90 days |
4. Storage on your device
Some things are kept in your browser's local storage rather than in a cookie. They stay on your device and are never sent to us as they are.
- Your preferences: light or dark theme, workspace layout, panel widths, worksheet answers in progress, and whether you have dismissed the getting-started checklist. These exist because you chose something, so they are not covered by the switch.
- Analytics counters: small entries that stop us counting the same page view or quota warning twice. These are covered by the switch, and turning it off clears them.
5. Product analytics
We use PostHog (EU region) to understand how the Service is used and to see errors. It is configured without browser persistence, so it writes no cookie and no local storage of its own, and session replay is off. The text and attributes of anything you interact with are masked before they are sent, page addresses are stripped of share tokens and content identifiers, and referring pages are reduced to their site of origin.
We do this under our legitimate interests in understanding, maintaining, and improving the Service. Turning optional cookies off above stops it for you, and you can also object by writing to privacy@withkyn.com.
6. What we do not do
We do not use advertising or cross-site tracking cookies, we do not load third-party tracking pixels, we do not build advertising profiles, and we do not sell your data. If we ever advertise in a way that needs a tracking pixel, we will ask for your consent first, through a banner, before setting it. This notice would be updated in the same change.
7. Questions
Write to privacy@withkyn.com. If you are in the UK and unhappy with how we handle your data, you can also complain to the UK Information Commissioner's Office (ICO).
Change log
- v1.0.0 · 29 July 2026 Initial cookie notice published: the full list of cookies and on-device storage, and a switch that turns every optional cookie off.