MODDABLE CHESS

One engine
Infinite rulesets

A modular chess engine that plays 74 variants on boards from 4×8 to 12×8. Zero dependencies. Pure JavaScript. Open source.

Play now Documentation GitHub
74 VARIANTS

Every variant, one engine

FOR DEVELOPERS

Five lines to a playable board

Load the scripts, create a game, render the board. The engine handles move generation, check detection, variant rules, and board rendering.

<script type="module">
  import MCE from 'https://chess.moddable.games/js/chess-engine.js';
  import 'https://chess.moddable.games/js/chess-moves.js';
  import 'https://chess.moddable.games/js/chess-play.js';
  import 'https://chess.moddable.games/js/variants/standard.js';
</script>
import { createGame, legalMoves } from './js/chess-engine.js';
import { makeMove, getStatus } from './js/chess-play.js';

const game = createGame('standard');
const moves = legalMoves(game);
makeMove(game, moves[0]);
console.log(getStatus(game));
<iframe src="https://chess.moddable.games/play/?embed=1&boardonly=1&variant=standard&theme=cosmic"
  width="480" height="480" frameborder="0"></iframe>
Read the docs Add a variant
BUILD WITH MCE

More than a variant picker

MCE is a full game development toolkit. Custom pieces, terrain, effects, AI, animation, and rendering — use it as the engine inside your own game.

♜
Custom Pieces

Define movement with declarative specs or full custom logic. Divergent move/attack, cannons, gapped slides, knight leaps.
♦
Terrain & Effects

Water, walls, lava — global terrain predicates. Timed effects with automatic expiry and undo support.
⚙
Game Controller

Full interaction loop: click handling, AI scheduling, undo/redo, multi-step turns, promotion UI. One function call.
☆
Custom Rendering

Replace tiles, pieces, and overlays. Add surround effects. Full SVG control with animations that just work.
Dungeon Chess — 4-player tactical combat built on MCE

Dungeon Chess uses MCE as an embedded engine — 4-player tactical combat with 22 unit types, terrain, and custom rendering. All game logic is MCE; the game adds only UI.

Play Dungeon Chess Read the guide API reference
AI INTEGRATION

Ask Claude to play chess

Connect in one command. Claude can analyze positions, generate puzzles, validate moves, and explain variant rules across all 74 chess variants.

claude mcp add --transport http moddable-tools https://tools.moddable.games/mcp
♔
Position Analysis

Engine evaluation with best move and principal variation for any variant.

♟
Puzzle Generator

Create mate-in-1 or mate-in-2 puzzles in standard or variant chess.

✓
Move Validation

Check if a move is legal with human-readable explanations of why not.

★
Variant Rules

Look up rules, board sizes, and descriptions for 74 chess variants.

View API Docs MCP Reference
MODDABLE ENGINES

Part of a family

Moddable Chess is one of several open-source game engines built with the same architecture: zero dependencies, embeddable, seeded RNG, and GitHub Pages deployment.

Moddable Hexmaps

Hex map engine for Nukes, Talisman, and Twilight Imperium. Canvas rendering, seeded RNG, terrain editing, and a plugin system for custom games.
All Engines

Browse all Moddable Games engines and tools at the main site.