Plugins

Game-family-specific logic. Each plugin handles all variants within its family through configuration, not code branching.

What plugins are

A plugin encapsulates the rules for a game family: legal move generation, capture mechanics, win/draw detection, and turn flow. The engine has 14 built-in plugins: backgammon, chess, draughts, go, hex, hop, the Landlord's Game, mancala, morris, race, reversi, shogi, tableau and xiangqi. Families without a plugin of their own name one of these in their rulebook; see Families on Shared Plugins.

Plugins receive configuration (from frontmatter) and produce behaviour. The same chess plugin handles standard, Fischer Random, Capablanca, and 72 other variants through different config parameters.

Plugin structure

A plugin is a factory function that returns a plugin object:

export function createMyPlugin(config = {}, context = {}) {
  return {
    sliceName: 'myGame',

    init(pluginConfig, { provide, request }) {
      // Set up initial state, register capabilities
      return { /* initial state */ }
    },

    getLegalMoves(state, topology, playerIndex) {
      // Return array of legal moves
      return []
    },

    applyMove(state, move, topology) {
      // Apply move, return new state
      // Return { state, continueTurn: true } for multi-action turns
      return { state: newState }
    },

    checkWin(state, topology) {
      // Return winner index, 'draw', or null
      return null
    },
  }
}

Universal hooks

All plugins implement from the same set of 11 hooks. No game-specific hooks exist.

Hook	Purpose
init	Initialise state, register capabilities
getLegalMoves	Generate all legal moves for current player
applyMove	Execute a move, return new state
checkWin	Detect win, draw, or ongoing
validateMove	Check if a specific move is legal
getScore	Numeric evaluation for AI
serialize	State to notation string
deserialize	Notation string to state
getMetadata	Piece lists, captured pieces, etc.
onTurnEnd	Post-turn cleanup (timers, clocks)
onGameEnd	Final state processing

State ownership

Each plugin owns a named state slice (its sliceName). Any plugin can read any slice, but only the owner can write to it. State must be JSON-serialisable.

The continueTurn mechanism allows compound turns: Morris mill removal, Backgammon multi-dice moves, Draughts forced capture chains.

Registry

Plugins register at packages/plugins/registry.js:

import { register, get, has, createFactory } from 'packages/plugins/registry.js'

// Register a custom plugin
register('myGame', { factory: createMyPlugin })

// Retrieve a factory
const factory = createFactory('chess')
const plugin = factory(variantConfig, context)

All 13 built-ins auto-register when packages/plugins/index.js is imported.

Adding a plugin

1. Create packages/plugins/my-game/ with src/my-game-plugin.js and index.js
2. Export your factory from index.js
3. Add the import + register call to packages/plugins/index.js
4. Write tests in packages/plugins/my-game/__tests__/