Villager Checkers

Opening a villager's trade screen shows a Play Checkers button that starts a game on a full board. The villager's trading level sets the strength of its play, so a Novice villager walks into traps while a Master villager converts the endings it wins. The player always moves red first, and items and commands are used only for setup, not during play.

The rules follow American and English draughts, including the less familiar one in which a man crowned in the middle of a jump stops instead of continuing as a king. Captures are compulsory, and a player who has a legal move but no pieces left loses. Draws are declared after a 40-move quiet rule or a threefold repetition. Resigning is done with a button that closes the board. If the player strays far from the villager, or the villager dies, or the player disconnects, the game is abandoned. The mod can be played for stakes or rewards, or simply for bragging rights.

The engine is written from scratch in pure Java, using a packed board of 32 playable squares, jump sequences that count as one indivisible move, and Zobrist hashing. Move generation has been checked against published perft counts up to depth 8. Fabric API is required, and the mod is published for Fabric only, for game versions 26.2 and 26.3. It runs on the client and the server, so both need it. The source code is open source under the MIT License.