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Fat Fritz 2 - free for all under the GNU GPL 3.0 license.

At last? Hmmm....

Although the picture above shows a man smiling sympathetically, I am not laughing at the time of writing this post.

It will be a rather short story about the power of Open Source, and while not as cheerful as the gentleman in the picture, it will probably have an optimistic ending... Anyway, decide for yourself :)

The Fat Fritz 2 chess engine was sold until recently, although it was actually Stockfish with altered neural network.

For readers less familiar with chess engines, Stockfish is a free open source chess engine under the GNU GPL 3.0 license. It is the result of many years of hard work by hundreds of people from all over the world. As a result, Stockfish is one of the strongest and maybe even currently the strongest chess engine on our planet.

The aforementioned license permits commercial use of the software, but this must be done in accordance with the applicable provisions of the license.

Quoting a post from the Stockfish blog:

"(...) Fat Fritz 2 and Houdini 6 are based on Stockfish, and ChessBase infringed on the license by not distributing these products as Free Software in accordance with the GPL. Their customers have not received the necessary information, namely the text of the GPL license covering these programs and the corresponding source code of these programs, to exercise the rights granted by the GPL. These rights include the right to reproduce, modify and distribute GPLed programs royalty-free."

The open source chess community has greeted with outrage the actions of ChessBase GmbH, which sold Fat Fritz 2 - reaping tangible financial profits of the product, which was in fact based on free Stockfish.

The case went to court with a lawsuit by the Stockfish Team.

On November 7, 2022, a settlement agreement between the parties was published, from which sales of the Fat Fritz 2 program have been halted and, quote:


  • Within eight weeks after the conclusion of this Settlement, Defendant shall, in order to improve compliance with license terms on Free and Open Source Software (FOSS), internally introduce the role of a "Free Software Compliance Officer" and list under the domain [] the products that contain the software Stockfish under the GPL-3.0 or other FOSS. If the respective licenses require the provision of the source code, the Defendant will enable a download of the source code by anyone from there.

  • Neural Networks offered by Defendant for use with Stockfish that are included in the compilation or dynamically loaded at runtime to initialize the data structures and logic of the Software must be subject to GPL-3.0 or a compatible license.


In short, the Fat Fritz 2 chess engine, based on a court settlement, became available under the GNU GPL 3.0 license along with the source code and the neural network.

This means that anyone interested can use the software in accordance with the aforementioned license. So is the case with the Stockfish chess engine.

GNU GPL 3.0 licenses (and others, such as LGPL 2.1) are documents - guarantees of the "freedom" of software. In vastly simplified terms, they stipulate that software released under such a license remains free and available to all. It is a violation of the license to attribute it or use it without meeting all the conditions included in the documents. It poses a danger to the integrity of the open-source community: it destroys the trust that is so vital in this environment.

"Open source" does not mean something inferior, less valuable, because it's free. That's a myth. A much bigger problem with the use of this type of software is abuse.

"Open source" is valuable software. Why? Because it is transparent. Anyone can have access, anyone can make changes, improve. And when it works according to specific and acceptable mechanisms, it can be successful - just like the Stockfish project, which brings together many committed and talented people.

Furthermore, it is a good thing that thanks to the consistency and determination of people from the Open Source community in asserting their rights, the case went to court, the settlement of which strengthened the community.

The conduct of ChessBase GmbH unfortunately has and will continue to have consequences: the trust of existing customers and potential customers has been damaged; the reputational damage will take many years to recover from, which could translate into financial results.

What's next?

ChessBase GmbH has begun to take care to meet the terms of the GNU GPL 3.0 license and has made the source code of Fat Fritz 2 and other software available at Other issues to be implemented by ChessBase GmbH are described in detail in the court documentation made available on the Stockfish website.

I would like to point out that the topic is not only about the Fat Fritz 2 chess engine... We were still talking about the Houdini 6 chess engine, and I won't even elaborate on the Fat Fritz 1 topic, it's material for a separate entry; I'll just add that also Fat Fritz 1 is free to download from is a blog that, although it has been running for only nine months, is visited by a lot of people every day, which is the result of thousands of hours of work to create it and fill it with content. For everyone and for free.

And that is why I perfectly understand the Developers of the Stockfish chess engine, who worked for years on their creation.

Sales of the aforementioned chess engines did not come by chance, of course. Marketing did its job, extolling what great, innovative and improved chess engines they are.

It's very sad that ChessBase GmbH violated the terms of the GNU GPL 3.0 license and used open source software source code without even signaling it beforehand. As you can see, the temptation is sometimes too strong, especially when big money is involved.

It's not that such open source software can't be used. You can, but you have to signal it and meet all the requirements that arise directly from the provisions of the license.

As we already know, now Fat Fritz 2 is a free open source chess engine.

I have prepared compilations of this engine for popular platforms. In addition to the source code, I have included documentation regarding this topic downloaded from the Stockfish webpage.

Fat Fritz 2 was sold only in versions prepared for use on Windows computers. However, below you will find this chess engine also for Macs and 32/64-bit Linux and Windows.

If you want, download and use it.

Although, it might be better if you give the latest Stockfish or Lc0 a chance, they are 100% original, stronger and do not pretend to be anything they are not.

That's the power of Open Source, don't you think? ;)

Fat Fritz 2 source code by Stockfish Devs and Albert Silver (neural network)

Download 7Z • 17.52MB

Linux arm32 & arm64 & x64 – Compiled by Darius

Download 7Z • 17.63MB
Download 7Z • 17.79MB

Mac Apple Silicon & Intel – Compiled by Darius

Download 7Z • 17.55MB
Download 7Z • 17.76MB

Windows x32 & x64 – Compiled by Darius

Download 7Z • 17.95MB
Download 7Z • 18.21MB


In the Files area you will find free chess engines for download.



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