Fat Fritz is not the Only Ripoff and now ChessBase is Getting Sued


The developers of the popular chess engine Stockfish formally filed a lawsuit against ChessBase GmbH this week. Due to repeated violations of Stockfish’s software license, the Stockfish devs have ultimately revoked ChessBase’s right to distribute Stockfish and derivative software. ChessBase has ignored orders to cease and desist and continues to sell software containing code that they have no right to distribute.

When we first discussed this subject, the focus was the lightly-edited Leela and Stockfish clones Fat Fritz 1 and Fat Fritz 2, which ChessBase tried to sell using exaggerated claims. After the public backlash, including articles from the three largest chess websites and comments by GM Hikaru Nakamura, ChessBase was forced to backpedal at a shocking pace. The claims of a “new #1 engine” were scrubbed from their website, Fat Fritz 2 DVDs that didn’t give proper attribution were quietly recalled, and the comment sections of ChessBase blog posts were closed.

However, Fat Fritz 1 and 2 are not the end of the complaints against ChessBase. The Stockfish devs go on to say that the ChessBase product Houdini also contains large amounts of Stockfish code, and are prepared to demonstrate it in court. It’s important to note through all this that you are allowed (and indeed encouraged) to use code from Stockfish. In fact, Lichess uses Stockfish heavily in various parts of our infrastructure. However, you will not see any angry blog posts or lawsuits as a result, because we fulfill all the terms of the license, notably publishing the source code of what we create using Stockfish, and making it clear that our users (you!) have the right to see, modify and redistribute it in turn. Conversely, ChessBase has concealed the origins of Houdini v6 and never provided the corresponding source.

Free open-source software offers essential freedoms that benefit developers and users alike, and those freedoms should have been extended to users of Fat Fritz 1, 2, and Houdini. Failing that, free-software licenses are only meaningful if they are enforced, making this an important case not only for Stockfish, but also for the open source community as a whole. We are happy that the Stockfish developers have the will and means to take action.

Read the official statement from the Stockfish team here.