As followers of my YouTube channel will know, I have been experimenting with a number of chess variants studied by Google DeepMind (together with ex-World Champion Vladimir Kramnik) in their interesting paper “Assessing Game Balance with AlphaZero: Exploring Alternative Rule Sets in Chess”. This paper can be viewed at https://arxiv.org/abs/2009.04374
I’ve put together a playlist of videos of what will eventually be 24 videos covering 3 variants: pawn sideways chess, Torpedo chess and self-capture chess. The playlist is available here: https://www.youtube.com/playlist?list=PLxhvNMc95Uo-TArwdqOh_3ZtBBiJUTXNz
While investigating the resources available for playing and analysing these variants, I came across the wonderful Fairy Stockfish engine and – with a little help from the kind people at the Fairy Stockfish Discord managed to get things working enough to run Fairy Stockfish on my own hardware and play games between 2 instances of Fairy Stockfish in openings of my own choice! Fairy Stockfish Discord is here: https://discord.com/channels/779317816897699850/791247944463417374
This blog post is a summary of those efforts, firstly so that I don’t forget it if I start up again with variants 😉 and secondly if anyone else is interested and needs a step-by-step guide for doing it!
Where can you play Google DeepMind chess variants?
At the time of writing (16th March 2025) there are just 2 places where you can play the variants. You can play against humans at https://www.chess.com/variants You can play against Fairy Stockfish without needing any configuration at the wonderful Fairy Stockfish playground hosted here: https://fairyground.vercel.app/index.html
It’s a little bit “clunky” in its usage but it gets the job done beautifully and I’m immensely grateful to the programmers for making this wonderful resource available! You can see a number of videos in the playlist in which I play against Fairy Stockfish in sideways chess using this interface!
Where can I download Fairy Stockfish?
That is a little confusing: all the normal places tend to point you to a version that predates the Google DeepMind paper which means of course that the variants we are looking for are not programmed (yet!) However, the latest version can be downloaded here:
Or if you’re brave and handy, you can compile the source code yourself from the main source location: https://github.com/fairy-stockfish/Fairy-Stockfish/tree/master/src
Just like the normal Stockfish, there is a wide range of NNUEs (neural nets) to supplement the engine’s strength in each of the variants it plays. The best networks are available here:
The general approach is pretty simple: you place the downloaded files together in one directory and in principle you’re ready to rumble!
But where do you rumble?
This is the tricky question: which GUI can you use for playing out these games? The only one I found that was useable was the venerable WinBoard! The key feature of this GUI is that it has a “Test legality” checkbox, which when unchecked basically believes anything you or your engine input! If ever you run into a problem, make sure you haven’t forgotten this!
The slight downside I need to mention here is that it doesn’t appreciate the en-passant rule in Torpedo chess which can leave the board looking rather messy, but that doesn’t stop the engines playing out the full game against each other!
You can download the “latest” version (latest being a very relative term – this version seems to be from 2015!) using the link provided on this page: https://fairy-stockfish.github.io/gui/ This link also provides the complete instructions for setting things up.
Note that you may receive a warning from Windows when downloading this file. The normal disclaimers as to care and duty for your own PC apply as always, but as far as I can judge, I haven’t been taken over by Russian bots since downloading and running this software!
I just unpacked the WinBoard zip file and put in a folder next to my Fairy StockFish files:
The only thing that remains after starting WinBoard is to configure your engines through the Engine / Edit Engine list dialog.
“Fairy-SF-PawnSideways” -fcp “fairy-stockfish_x86-64-bmi2.exe” -fd “..\FairyFish” /variant=pawnsideways -firstOptions “EvalFile=pawnsideways-68b37e5c25b0.nnue”
“Fairy-SF-Torpedo” -fcp “fairy-stockfish_x86-64-bmi2.exe” -fd “..\FairyFish” /variant=torpedo -firstOptions “EvalFile=torpedo-25da2c94c6cb.nnue”
The above examples configure engines for pawn sideways chess and Torpedo chess.
As always, it’s a little fiddly to get it right, but with a couple of minutes of experimentation it should all work fine.
To play a game between – for example – 2 Fairy StockFish pawn sideways engines, you first have to go to Engine / Load First Engine and select the appropriate engine:
You then repeat the same step through Engine / Load Second Engine.
And then you just let the guys fight it out through Mode / Two Machines
One useful feature is the Edit Game Mode. You can set up a starting position you want, and then switch to Two Machines to let the engines fight things out from specific openings! I have more than 50 long-play (40 moves in 2 hours) games from various openings in different variants and it’s really interesting to see!
How do I know exactly which variants Fairy Stockfish supports?
To know which text to put in the Engine / Edit Engine list dialog, the simplest way is to start a command prompt and navigate to the directory in which you put your Fairy Stockfish executable.
Start the executable and then type uci
Under option name UCI_Variant you can see all the supported variants!
Hope this helps anyone interested in variants and huge thanks to the Fairy Stockfish team for making such a wonderful resource available to everyone! Never ceases to amaze me what is possible and available out there!