Developer Guides

Why Four Guides?

The engine has three layers of extension points, and no single variant uses them all:

• Custom pieces — new movement patterns, attack functions, piece registration
• Game hooks — action moves, turn logic, move filtering, board mutations
• Effects system — timed status effects, square-based state, automatic expiry

Guides 1–3 each target one layer in isolation, building a variant plugin from scratch. Guide 4 uses all three layers together and adds the consumer APIs — game controller, terrain, custom rendering, and unit templates — to build a complete standalone game on the engine.

Guide 1: Orda Chess — Custom Pieces

Build three custom pieces with divergent movement (move one way, capture another). Covers:

• MCE.registerPiece() — define new piece types with movement and attack logic
• genMoves(g, from, side) — generate pseudo-legal moves (slides, jumps, divergent patterns)
• attacks(g, from, target) — check detection for custom pieces
• pieceRoles — map piece characters to handlers
• Asymmetric FEN — different armies for each side

Start the Orda Chess guide

Guide 2: Crazyhouse — Action Moves and State

Build the most popular variant online. Captured pieces go into your hand and can be dropped back. Covers:

• init — initialize custom game state (hand arrays)
• moveFilter — generate non-standard moves (drops) alongside normal moves
• afterMove — respond to moves (place drops, capture to hand)
• MCE.mutateBoard() — board changes with automatic undo
• restoreState — restore custom state for AI search
• evaluate — teach the AI to value hand pieces
• statusText — display custom information to the player

Start the Crazyhouse guide

Guide 3: Poison Chess — Effects System

Build a variant with timed square effects. Capture squares become toxic, destroying pieces that land on them. Covers:

• MCE.addEffect() — create timed effects on squares
• MCE.hasEffect() — query effects during move filtering
• MCE.tickEffects() — automatic duration countdown
• MCE.mutateBoard() — destroy pieces with undo support
• moveFilter — restrict movement based on effects
• evaluate — score positions considering effect proximity

Start the Poison Chess guide

Guide 4: Dungeon Chess — MCE as a Game Subsystem

Build a complete standalone game on MCE — 4-player tactical combat with 22 custom unit types, terrain, effects, capture interception, multi-step turns, and fully custom rendering. Covers:

• MCE.buildUnitHandler() — declarative move specs with the unit template system
• ownershipMode: 'pieceData' — unlimited unit types via a single piece character
• terrainSkip — global terrain predicates for move generation
• beforeMove — capture interception (cancel/redirect captures)
• afterMove + MCE.mutateBoard() — board mutations with undo
• turnLogic + pendingAction — multi-step turns
• positionKey — custom hash for pieceData-based games
• MCE.createGameController() — full interaction loop with AI, undo, animation
• tilePainter / pieceProvider / afterRender / surroundRenderer — custom rendering pipeline
• onSquareClick / onAnimateMove — controller interaction callbacks

Start the Dungeon Chess guide

Which Guide Do I Need?

Reference

• API Reference — every method on the MCE namespace
• Plugin Reference — all config flags and hooks for registerVariant()