1. Introduction
This Privacy Policy explains how Chess Book (“we”, “us”, or “the Extension”) collects, uses, and shares information when you install and use the Chess Book browser extension on supported chess websites (currently chess.com).
By installing or using Chess Book, you agree to this Privacy Policy. If you do not agree, please uninstall the Extension.
2. Who we are
Chess Book is operated by Chess Book. For privacy questions, contact us at privacy@chessbook.app.
3. What Chess Book does
Chess Book provides in-page chess analysis features, including:
- Local engine analysis (Stockfish running in the extension)
- Evaluation displays (eval bar, eval graph, move feedback)
- Optional product messages shown inside the extension UI
- Anonymous product analytics used to improve the Extension
4. Information we collect
4.1 Information stored only on your device
The Extension may store locally in your browser:
- A randomly generated extension user ID (UUID)
- Your extension settings (for example: power switch, display options, engine strength)
- Saved game history you play while the Extension is active (non-bot games)
- Which product messages you dismissed
- Cached product messages fetched from our servers
This local data stays in your browser storage unless you clear it or remove the Extension.
4.2 Information sent to our servers
When the Extension is online, it may send limited data to our backend at sentinel.chessbook.app for messaging and analytics.
Analytics events may include:
- start — browser language, your rating, opponent rating
- move — browser language, the move you played (SAN), selected UI options, engine strength setting
- over — browser language, ratings, full move list for the game, and result (win / lose / draw)
Requests are authenticated with your extension user ID and a signed header. We do not ask you to create an account to use the Extension.
4.3 Information we do not intentionally collect
- We do not collect your chess.com password
- We do not sell your personal information
- We do not use the Extension to show third-party advertising networks
- We do not collect precise device location via GeoIP on the client
5. How we use information
We use the information described above to:
- Provide and operate Chess Book features
- Deliver relevant in-extension product messages
- Understand usage and improve reliability, performance, and product quality
- Diagnose errors and prevent abuse of our API
6. Legal bases (EEA/UK users)
If applicable, we process data based on:
- Legitimate interests — operating, securing, and improving the Extension
- Consent — where required by law for optional analytics or similar processing
- Contract / service delivery — providing the features you install the Extension to use
7. Sharing of information
We may share information with:
- Infrastructure providers that host our API and databases (for example cloud hosting / database providers), solely to operate the service
- Authorities if required by law or to protect rights, safety, and security
Chess Book runs as a content script on chess.com pages. Chess.com is a separate service with its own privacy policy. We are not responsible for chess.com’s practices.
8. Data retention
Local extension data remains until you clear browser/extension storage or uninstall Chess Book. Server-side analytics and operational logs are retained only as long as needed for the purposes above, then deleted or aggregated.
Exact retention periods may vary by event type and legal requirements. Contact us if you want details for your region.
9. Security
We use reasonable technical measures to protect data in transit (HTTPS) and to authenticate extension API requests. No method of transmission or storage is 100% secure.
10. Your choices and rights
- You can disable or uninstall the Extension at any time in your browser
- You can clear extension storage from browser settings / developer tools
- Depending on your location, you may have rights to access, correct, delete, or restrict processing of personal data
To make a privacy request, email privacy@chessbook.app and include enough information for us to locate your extension user ID if relevant.
11. Children’s privacy
Chess Book is not directed to children under 13 (or the minimum age required in your country). We do not knowingly collect personal information from children. If you believe a child has provided data through the Extension, contact us and we will take appropriate steps.
12. International transfers
Our servers and subprocessors may be located in countries other than yours. Where required, we use appropriate safeguards for cross-border transfers.
13. Changes to this policy
We may update this Privacy Policy from time to time. The “Last updated” date at the top will change when we do. Continued use of the Extension after an update means you accept the revised policy.
14. Contact
Privacy questions or requests:
Email: privacy@chessbook.app
Website: https://chessbook.app