Privacy

Your book is yours. We don't even see it.

Last updated October 11, 2026

The short version: Cairn has no accounts, no analytics, no ads and no trackers. Everything you write is saved in your own browser and never sent to us. Pip runs entirely on your device. If you choose to add your own OpenRouter key, the messages you send Pip go straight from your browser to OpenRouter. They never pass through us.

What we collect

Nothing about you. The site has no sign-up, no cookies, no analytics, no tracking pixels, no fingerprinting, and no third-party scripts. A strict Content Security Policy enforces this: the only outside address this site's pages are allowed to contact is OpenRouter, and only if you turn that feature on yourself.

The site is served by Cloudflare. As with any website, Cloudflare's network processes the technical details of each request (such as your IP address and browser type) to deliver the page and protect against abuse. We don't add logging of our own, and we don't use Cloudflare's visitor analytics. See Cloudflare's privacy policy for how they handle network data.

Where your writing lives

Your chapters, word counts, streak, settings and chat with Pip are stored in your browser's localStorage on this device, under this site's address. They are not uploaded, synced or backed up by us. That has two consequences you should know about:

Other people who use this browser profile can read it. Use your own profile, or erase your data when you're done (Settings → Erase everything on this device).
Browsers can delete site data. Clearing your history or site data deletes your book. Some browsers, Safari in particular, may also remove data for sites you haven't visited in a while. Cairn asks your browser to keep its storage, but that request isn't guaranteed. Export your book regularly (Export → Whole book). It's one Markdown file.

How Pip works

By default, Pip is a "Markdown Language Model": a small library of notes written in Markdown, plus a tiny program that picks the right note for the moment by matching keywords. Both download with the page and run in your browser. Your messages to Pip and your manuscript are never sent anywhere. Pip's guidance is original writing advice in our own words.

Optional: your own OpenRouter key

In Settings you can paste an API key from OpenRouter so that Pip answers with a language model of your choice. If you do:

Your key is stored only in this browser's localStorage. It's never sent to us, and we have no server that could receive it.
When you send Pip a message, your browser sends it directly to openrouter.ai, together with Pip's instructions, a few notes from Pip's library, your recent chat with Pip, and simple numbers (words today, daily goal, streak, chapter count).
Your manuscript is not sent, unless you turn on "Share the paragraph I'm working on". Then the paragraph your cursor is in (up to about 1,500 characters) goes with each message.
OpenRouter and the model provider you pick handle that request under their own terms and privacy policies. Usage is billed to your OpenRouter account.
"Forget key" in Settings deletes the key from this browser. You can also revoke it from your OpenRouter account at any time.

Anyone with access to this browser profile, or any script running on this site, could read a key stored in localStorage. This site loads no third-party scripts, but if that risk matters to you, use a key with a low spending limit.

Children

Cairn doesn't collect personal information from anyone, including children.

The iPhone app

The upcoming iPhone app will have its own privacy policy and App Store privacy label, published here before it launches.

Changes

If this policy changes, we'll update this page and the date at the top. We won't add analytics or trackers to the web version.