For example, here is a 4x6 chess position. Black to move. How can I determine who is winning, and by how much?

FEN: KBNR/1P2/P1P1/2pp/p3/kbnr


Chess variant on a small board. Standard rules apply with the following changes:

  • Starting position and number of pieces are changed
  • Pawns have no double-move option
  • There is no castling
  • 4
    To the person who downvoted the question, I expect you to give a viable answer of either my question or reason for your downvote. It will help me learn. Thanks.
    – AyushDwi
    Mar 6, 2022 at 19:08
  • 4
    I'm not sure I understand the question. If this is truly a question about evaluating this position, why would you not analyze this like any other position, i.e. by looking at the position, calculation, and applying the usual chess principles that you already know? Or is this a question about how to get a computer to evaluate such a position? Mar 6, 2022 at 22:59
  • 3
    As @Dargscisyhp asks/comments: do you want advice on how to use standard principles to evaluate it, or, instead, how to get a chess engine to evaluate it (in some understandable way)? Can you clarify? Mar 6, 2022 at 23:21
  • 5
    What are the rules for 4x6 chess? That is: do pawns start with a double-move option; is there Castling? May one promote to a Queen, or only to one of RBN? (Whatever the precise rules are, I'd expect that any position on such a small board can be analyzed out to either forced mate or forced draw, so there's no "by how much": you're either winning or not.) Mar 7, 2022 at 2:50
  • 1
    when i see the position i feel like black is better due to space advantage but im not quite sure. for example moves like e3 can be met with something like Rxe3
    – cmgchess
    Mar 7, 2022 at 4:11

1 Answer 1


Fairy-Stockfish is a nice Stockfish fork that can handle a variety of Chess variants. Find and install it following the directions here.

Create a file called variants.ini. Paste the following into there.

maxRank = 6
maxFile = d
promotionRank = 6
startFen = rnbk/pppp/4/4/PPPP/RNBK w - - 0 1

Alternatively, download and save the linked file somewhere on your computer, which comes with the 4x6 variant along with several others.

You have a variety of choices for which front end to use. I am going to use Xboard. If you happen to be on Windows, you can use Winboard and the procedure should be fairly similar.

If you've chosen to install Xboard/Winboard, you can use the following procedure. Click engine on the menu bar up top and then go to edit engine list. Modify and add the following line

"Fairy-SF" /variant=4x6chess -fcp "/path/to/fairy-stockfish-binary load /path/to/variants.ini"

Here you should modify your /path/to/fairy-stockfish-binary to wherever that binary/executable exists and modify your /path/to/variants.ini to wherever you earlier created/saved your variants.ini file.

You can now go back to Engine in the menu bar and select Load New First Engine, selecting the engine you just added. You should now see something like the following image.

enter image description here

You can play the engine from this point if you want. Alternatively, you can paste in a position and ask the engine for analysis. To do the latter with your initial position, copy the following fen to your clipboard:

rnbk/3p/pp2/1P1P/2P1/RNBK w - - 0 1

On the Xboard/Winboard menu bar select Edit and then select Paste Position. The position should now be in Xboard. Finally you can select mode from the menu bar and select analysis mode. This should give you what you want:

enter image description here

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