Privacy policy

Last updated October 18, 2026

Zero to Frontier is an online book about machine learning and AI. You can read it without an account. This page explains what we keep when you sign in or pay, and how to remove it.

What we collect

When you sign in with Google, we receive your name, email address, and profile picture.
If you are signed in, we save your reading progress, solved exercises and their times, saved exercise code, pinned tutor answers, tutor chats, notes, Playground notebooks, review schedule, and model choice to your account.
If you attach a link or a PDF to a note, our server fetches it to read its title and size, and again when you ask for a summary. We keep the link, its title, and any summary in your note, not the file.
If you buy a plan or a top-up, we keep a record of the plan, the credits, and the amount. Card details go straight to Stripe and never reach us.
If you write to us through the contact form, we keep your message and email address so we can reply.

If you are not signed in, nothing about your reading is stored, not even on your device.

AI features

When you use an AI feature (the tutor, the coding assistant, Notes, or the Playground), your question and what it is about (the section you are reading, your code, your note, or an attached document) are sent to the model you picked to produce the answer. Gemini models are run by Google, Claude models by Anthropic, and GPT models by OpenAI. These providers process the request under their API terms, which do not allow them to train on it. Signed-in readers' tutor chats are saved to their account so they can continue them, and can be deleted at any time.

Who processes your data

Google (Firebase and Google Cloud) hosts the site, signs you in, and stores your account data.
Google (Gemini), Anthropic (Claude), and OpenAI (GPT) answer AI questions, depending on the model you pick.
Stripe and its Link service handle payments, receipts, and sales tax.
Resend delivers emails about contact messages to us.

We do not sell your data, show ads, or use analytics trackers. The only cookie we set keeps you signed in.

Deleting your data

Open your Account page and use Delete account. It cancels any plan right away and permanently erases your progress, pins, saved code, chats, notes, notebooks, credits, payment records with us, and your sign-in account. Stripe keeps the payment records the law requires it to keep.

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