Privacy Policy

Last updated: October 10, 2026

MasterGuess (masterguesschess.com) is a free, non-commercial chess study site. This page explains what data it collects, why, and what you can do about it. The short version: it collects as little as it needs to run, it never sells or shares your data for advertising, and you can ask for everything to be deleted at any time.

Using the site without an account

You can browse the library and study games without signing in. Your study progress, notes, and settings are then kept only in your own browser's local storage and never leave your device. Clearing your browser data removes them.

Chess engine analysis runs entirely in your browser. The positions you analyze are not sent to us.

If you sign in

Signing in uses your Google account. When you do, we store:

• Your email address and Google's account identifier for you, to recognize you when you return.
• A sign-in session, kept in a cookie in your browser. It lasts up to 90 days, or until you sign out.
• Your study progress for each game, including your guesses, variations, and any notes you write.
• The games you mark as favorites.

We only ask Google for your email address and identity. We do not get your Google password, contacts, or any other Google data.

If you link a lichess account

Linking lichess lets you send finished studies to your lichess studies. We store your lichess username and a lichess access token, encrypted, and use it only to list your studies and add the chapters you choose to send. You can unlink lichess from your account page at any time, which deletes the token.

Analytics and session recordings

We use PostHog to understand how the site is used and to find bugs. It records:

• Pages you visit, buttons you click, and features you use (for example, guesses graded or studies completed).
• Errors that happen in your browser or on our server.
• Session recordings: a replay of how the page changed while you used it, such as clicks, scrolling, and moves on the board. Text you type into fields is masked while you type it, but notes you have saved can appear in recordings wherever the page displays them.
• Basic technical details: browser, device type, and approximate location derived from your IP address.

If you are signed in, our server's records of your requests are tied to an internal account number, not your email address. PostHog stores this data in the United States.

Who handles your data

We do not sell your data or share it for advertising. These services process it on our behalf:

• Amazon Web Services hosts the site and its database in the United States.
• Cloudflare carries all traffic to the site.
• Google handles sign-in.
• PostHog handles analytics, as described above.
• Lichess receives the studies you choose to send there.

Cookies and local storage

The site uses one cookie to keep you signed in. Your browser's local storage holds your settings, your progress when you are signed out, and PostHog's identifier for your browser. There are no advertising cookies.

How long data is kept, and deleting it

Account data is kept until you ask for it to be deleted. To delete your account and everything tied to it (progress, favorites, and any linked lichess token), or to ask what we hold about you, email [email protected] from the address you signed in with. Requests are handled within 30 days.

Children

The site is not directed at children under 13 and does not knowingly collect data from them.

Changes

If this policy changes, the date at the top will change with it. Significant changes will also be noted on the site.

Contact

Questions about this policy: [email protected].