Mons rules engine

Dependency-free TypeScript rules for Super Metal Mons. The ESM-only package runs in browsers, Web Workers, Node.js, and Firebase Cloud Functions.

Install

npm install mons-rules

Use

import { Game, GameVariant, type Input } from "mons-rules";

const game = new Game({ variant: GameVariant.Classic });
const inputs: Input[] = [
  { kind: "position", position: { row: 10, column: 5 } },
  { kind: "position", position: { row: 9, column: 4 } },
];

const preview = game.preview(inputs);
if (preview.kind === "complete") {
  game.play(inputs);
}

const suggestion = game.suggestMove("pro");
if (suggestion !== undefined) {
  game.play(suggestion.inputs);
}

const restored = Game.fromFen(game.toFen());

preview resolves typed inputs without mutation. play and playFen apply only complete legal moves. toFen serializes canonical game state and Game.fromFen restores it.

Fast, Normal, and Pro automove search is cooperatively time-bounded. Exact moves can vary with runtime timing, but returned suggestions are complete, legal, and do not mutate the source game.

Published JavaScript targets ES2022 and automove uses the Web-standard performance.now() clock. Node.js 22.13 through 22.x, or Node.js 24 or newer, is required for Node consumers and repository tooling.

Validate

npm run check

Maintainer boundaries and immutable-data rules are in docs/architecture.md on GitHub.

Release

npm run bump
npm run publish -- --check-only
npm run publish