KKFChess can play some chess variants, the support variants are:
| Variant | Console Mode | Winboard Mode |
| Regular (Normal) | This is the default game type. Use "new" to start a new regular chess game. | Winboard without any "-variant" command or with "-variant normal". |
| Wild 1 | Start a new regular chess game then use "fen" or "fen<" to setup the board using a FEN string. | Use Winboard's position editing function. |
| Suicide 2 | Use "suicide" or "variant suicide" to start a new suicide chess game. | Winboard with "-variant suicide". |
| Crazyhouse | Use "crazy", "crazyhouse" or "variant crazyhouse" to start a new crazyhouse game. | Winboard with "-variant crazyhouse". |
| Atomic | Use "atomic" or "variant atomic" to start a new atomic chess game. | Winboard with "-variant atomic". |
| Losers | Use "losers" or "variant losers" to start a new loser chess game. | Winboard with "-variant losers". |
Loading a PGN game with the tag "Variant" will also change the game type.
Suicide Chess is played using FICS rules.
1. KKFChess only knows normal castling moves hence it does not support Fischer's Random nor d-file castling. When playing on an ICS, KKFChess only plays wild type 2, 3 or 4.
2. KKFChess follows the suicide chess rules of FICS.
KKFChess' implementation of variant rules are the same as most ICS, except for suicide which uses FICS rules.