Terms of Service

Last updated 25 May 2026

By using OpenBook you agree to these terms. They're meant to be readable, not lawyered.

1. The service

OpenBook is a free chess opening trainer that uses your Lichess account to sign in and the Lichess Opening Explorer to show move statistics. We may add, change, or remove features at any time.

2. Lichess account

OpenBook signs you in with Lichess. By using OpenBook you also agree to Lichess's terms.

3. Acceptable use

Don't:

Try to gain unauthorized access to other users' data.
Scrape the app or its API in ways that disrupt service.
Attempt to reverse-engineer rate limits or other protections.
Use the app to violate any law or Lichess's own terms.

4. Your data

You own the repertoire, notes, and practice data you create. We don't sell it. We don't share it with anyone other than the infrastructure providers we use to run the service (see our Privacy Policy). You can export everything (menu → Export → JSON) or delete your account (menu → Delete account) at any time.

5. Opening data

Move statistics come from the Lichess opening database, which is released under CC0.

6. Open-source software

The position evaluation shown in Build mode (the eval bar and the green "best move" star) is computed in your browser by Stockfish, the open-source chess engine, via stockfish.js. Stockfish is free software licensed under the GNU General Public License v3; its source is available at github.com/official-stockfish/Stockfish. OpenBook bundles an unmodified Stockfish build and is not endorsed by the Stockfish project.

7. Termination

You can delete your account at any time. We may suspend or terminate accounts that violate these terms, abuse the service, or put other users at risk.

8. No warranty

OpenBook is provided "as is." It may go down, lose data, or behave unexpectedly. Back up anything you care about (menu → Export → JSON).

9. Limitation of liability

To the maximum extent permitted by law, OpenBook and its operator are not liable for any indirect, incidental, special, or consequential damages, or for lost data, lost time, or lost ratings, arising from your use of the service.

10. Changes

We may update these terms. If we change something material, we'll update the date at the top of this page. Continued use after a change means you accept the updated terms.

11. Contact

Questions or problems? Email feedback@openbookchess.com.