Privacy Policy

Last updated 7 September 2026

This Privacy Policy explains how Sad Coder, Inc. (Sad Coder, we, us, or our) handles personal data when you use Tidemarks, including the reader at app.tidemarks.io, the syncing service behind it, and its MCP server (collectively, the Service).

Sad Coder is the controller of personal data described in this policy unless we state otherwise. Our business and privacy contact details are:

Sad Coder, Inc., 5F., No. 50, Zhongyang 7th St., Xindian Dist., New Taipei City 231014, Taiwan — contact@tidemarks.io

This policy does not govern a third party’s independent processing, including Paddle’s transaction processing or an agent or client you choose to connect.

The short version

Without an account, we hold nothing. Tidemarks reads epub files in your browser. The books you import, the highlights and notes you write, and where you are in each book are stored on your own device and are never sent to us. There is no analytics script, no advertising, and no account to create.

With an account, we hold only the books that are syncing. A free account syncs three books; a paid plan removes that limit. A book is either entirely on the server or not on it at all — there is no halfway state where we have the title but not the file. Every other book on your device stays there, and we never learn it exists.

What we hold when you have an account

Your account. Your email address, and the passkeys registered to the account. We use these to let you in and to reach you about the Service. A sign-in code is short-lived and can be used once; we keep a record that it was sent, with the address it went to, because that record is how we limit how often codes can be requested. Those records are cleared once they are older than that limit.

The books that are syncing. For each one: the epub file exactly as you imported it, its cover, its title and author, your reading position, your highlights and notes, and your reading sessions — the times at which you read it, which the reader uses to estimate how long a chapter will take you.

Your subscription state. Whether the account is paid, and an identifier that lets us open Paddle’s customer portal for you. We never see your card. Paddle collects and holds payment details as merchant of record; see Paddle’s privacy notice.

Ordinary server logs, kept briefly for security and debugging.

What we do not do

These are commitments, not current settings:

• We do not scan the contents of your books, and nothing about what you read feeds a recommendation, a profile, or a model.
• We do not deduplicate. Two people who import the same book have two separate copies on the server, byte for byte. Your copy is yours.
• We never publish a link to a book. Every file is streamed through a request that checks it is yours first; there are no signed URLs and no public addresses.
• We do not sell personal data, and we do not share it for advertising.
• We use no third-party analytics and set no advertising cookies.

Why we are allowed to hold it

Where the GDPR or a similar law applies, we rely on: performance of a contract for running your account and syncing your books; legitimate interests for keeping the Service secure and working; and legal obligation where a law requires us to keep something. Where consent is required, we ask for it and you can withdraw it.

Who else sees it

Only the processors it takes to run the Service:

• Cloudflare, which hosts the Service and stores the database and files.
• Resend, which delivers sign-in and service emails.
• Paddle, as merchant of record for payments. Paddle is an independent controller of the transaction data it collects.

We do not send your books, highlights or notes to any of them beyond what hosting requires, and we share personal data with a public authority only where the law requires it.

An agent you connect

Tidemarks has an MCP server, so an AI agent you authorize can read your books, notes and reading positions. It sees only the books that are syncing, never one that is only on a device, and never a frozen one. What that agent then does with what it reads is governed by whoever operates it, not by this policy. You can revoke access by removing the authorization.

How long we keep it

Your account and its syncing books are kept while the account exists.

A frozen book — one above your sync limit after a subscription ends — is kept for at least 24 months. The copy on your own devices is untouched by this, and always has been.

A book you delete stops syncing as soon as the deletion reaches us, and an agent can no longer read it. Its file is removed from our storage when we next sweep for orphaned files; we do not promise that this happens the same day. If you want a book gone from the server now, write to us.

Sign-in records and the sign-up list hold email addresses, as described above, and ordinary server logs are kept briefly for security and debugging.

Your rights

Depending on where you live, you may have the right to access, correct, delete, restrict, or object to our processing of your personal data, to withdraw consent, and to receive your data in a portable form. To exercise any of these, write to contact@tidemarks.io; we may need to verify that you control the account’s email address.

Two of these you can do without asking us. Export is built into the reader: the account pane writes your books, notes and reading positions to a file you keep, and the epub in it is the file you imported, unchanged. It writes the books this device has the file for — a book that is syncing but has not been opened on this device yet needs opening once first. Deleting a book in the reader removes it from the server as well, on the terms in the retention section above.

To close an account entirely, write to us and we will delete it and everything the server holds for it. There is no self-service button for this yet.

You may also complain to your local data protection authority.

Children

The Service is not directed at children and we do not knowingly collect personal data from them. If you believe a child has given us personal data, write to us and we will delete it.

International transfers

The Service runs on Cloudflare’s network, so data may be processed in a country other than yours. Where a transfer needs a safeguard under the GDPR or a similar law, we rely on the appropriate mechanism, such as the European Commission’s standard contractual clauses.

Security

Books and covers are streamed only after the request is checked against the account that owns them. Sign-in uses passkeys or a one-time code sent to your email address, so control of that mailbox is control of the account — keep it secure. No service can promise perfect security, and we do not.

Changes

We may update this policy. We will post the new version and update the date above, and for a material change we will give reasonable notice through the Service or by email.

Contact

Questions about this policy or about your personal data: contact@tidemarks.io, or the Sad Coder address at the top of this page.