Chess

100 chess variants with AI, embed support, and a headless SDK for server-side consumers.

Embed via iframe

Drop a board into any page with a single iframe. The embed is fully responsive and touch-ready.

<iframe
  src="https://engine.moddable.games/play/?embed=1&variant=standard"
  style="width:100%;max-width:560px;aspect-ratio:1/1;border:none"
  title="Play Chess"
></iframe>

URL parameters

Param	Values	Default
embed	1	Required for embed mode
variant	Any variant key	standard
opponent	ai | human	ai in embed
difficulty	beginner | easy | medium | hard | expert	medium
color	white | black	white
pieces	Piece set ID	mce-fairy-complete
flipped	1	Board orientation

postMessage control

Control the embed without reloading the iframe. Send messages to iframe.contentWindow:

// Change variant
iframe.contentWindow.postMessage({ type: 'chess:setVariant', variant: 'atomic' }, '*')

// Change difficulty (also activates AI)
iframe.contentWindow.postMessage({ type: 'chess:setDifficulty', difficulty: 'hard' }, '*')

// Switch between human/AI
iframe.contentWindow.postMessage({ type: 'chess:setOpponent', opponent: 'ai' }, '*')

// Game controls
iframe.contentWindow.postMessage({ type: 'chess:newGame' }, '*')
iframe.contentWindow.postMessage({ type: 'chess:undo' }, '*')
iframe.contentWindow.postMessage({ type: 'chess:flip' }, '*')

// Change piece set
iframe.contentWindow.postMessage({ type: 'chess:setPieces', set: 'mce-chess' }, '*')

// Change board theme
iframe.contentWindow.postMessage({ type: 'chess:setTheme', theme: 'cosmic' }, '*')
// Themes: classic, cosmic, wood, marble, neon, minimal, transparent

Events from embed

Listen on the parent window for game events:

window.addEventListener('message', (e) => {
  switch (e.data.type) {
    case 'chess:ready':
      // { variant, fen }
      break
    case 'chess:move':
      // { from, to, fen, variant }
      break
    case 'chess:status':
      // { text: 'white'|'black'|'draw', gameOver: true, variant }
      break
  }
})

Chess SDK

Headless SDK for server-side tools, APIs, and direct browser consumption.

import {
  listVariants,
  createGame,
  getLegalMoves,
  analyzePosition,
  getGameStatus,
  renderSvg,
  createAI,
} from 'moddable-engine/play/sdk'

listVariants(group?)

Returns all registered variants with metadata.

const all = listVariants()          // 100 variants
// [{ key, label, group, board, description, rule }]

getLegalMoves(variant, fen?)

Returns all legal moves in algebraic notation.

const moves = getLegalMoves('standard')  // starting position: 20 moves
// [{ from: 'e2', to: 'e4', capture: false, promotion: null, flag: null }]

analyzePosition(variant, fen?, depth?)

AI evaluation with best move.

const result = analyzePosition('standard', null, 4)
// { bestMove: 'e2e4', evaluation: 0.3 }

renderSvg(variant, fen?, opts?)

Renders a board position as an SVG string. No DOM required.

const { svg, rows, cols } = renderSvg('capablanca')
// svg = '<svg xmlns="..." ...' (14KB, self-contained)

const custom = renderSvg('standard', 'rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1')

getGameStatus(variant, fen?)

const status = getGameStatus('standard', 'some-fen')
// { status: 'active', gameOver: false, turn: 'white', inCheck: false }
// or: { status: 'checkmate', gameOver: true }

Game state management

const game = createGame('chess', 'atomic')
const moves = game.getLegalMoves()
game.applyMove(moves[0])

Variants

100 variants registered and playable. Use the key as the variant URL parameter or SDK argument.

Key	Board	Distinguishing rule
standard	8×8	Standard FIDE rules
absorptionChess	8×8	Capturing piece gains the victim's movement abilities
almost-chess	8×8	White's Queen replaced by a Chancellor (R+N)
amazon-chess	8×8	Queens replaced by Amazons (Q+N)
andernachChess	8×8	Capturing piece changes colour
antichess	8×8	Captures mandatory; first to lose all pieces wins
asean	8×8	Southeast Asian rules: Makruk-family pieces, rank-6 promotion
atomic	8×8	Captures explode all adjacent non-pawn pieces
benedictChess	8×8	No captures; attacked enemies convert to your colour
berolinaChess	8×8	Pawns move diagonal, capture straight (inverted)
berserkChess	8×8	Check grants one bonus move
birds-chess	8×10	1874 variant with Guard (R+N) and Equerry (B+N)
breakthrough	7×7	Pawns only; first to reach the far rank wins
brusky	hex	Horizontal 84-hex board, 10 pawns per side
byzantine-chess	4×16	Circular board, Shatranj pieces, stalemate wins
capablanca	8×10	Archbishop (B+N) and Chancellor (R+N) on a wider board
carrera	8×10	1617 variant with Champion (R+N) and Centaur (B+N)
chancellor-chess	9×9	Chancellor (R+N) added on 9×9
chaturanga	8×8	Ancient Indian ancestor; weak counsellor, leaping elephant
checklessChess	8×8	Cannot give check unless it is checkmate
chess960	8×8	Randomised back rank (960 positions)
chigorin	8×8	White's Bishops replaced by Knights
circular-chess	4×16	64 squares in 4 concentric rings; no castling
codrus	8×8	Win by getting your own King captured
courier	8×12	Medieval 1202 variant on a 12-wide board
crazyhouse	8×8	Captured pieces switch sides and can be dropped
cylinder-chess	8×8	a-file wraps to h-file
darkChess	8×8	Total fog; only see your own pieces' squares
de-vasa	hex	81-hex rhombus board
diana	6×6	No queens or knights; bishops and rooks only
diceChess	8×8	Die roll constrains which piece type must move
displacementChess	8×8	Swap positions with adjacent friendly pieces
duckChess	8×8	Place a blocking duck on any empty square after each move
einsteinChess	8×8	Non-capturing moves demote; captures promote
empire	8×8	Asymmetric: FIDE Kingdom vs Empire dynasty
endgame-chess	8×8	Kings and pawns only from move one
extinction	8×8	Lose any piece type entirely and you lose
fiveCheck	8×8	Five checks wins
fogOfWar	8×8	See only squares your pieces can move to
giveaway	8×8	Forced captures; stalemate is a loss
glinski	hex	91-cell hexagonal board; three bishops per side
grand	10×10	Marshal and Cardinal; pawns start on rank 3
gridChess	8×8	Moves must cross a 2×2 grid line
half-chess	4×8	4-rank board; armies start adjacent
hexapawn	3×3	Six pawns; reach far rank wins
hoppel-poppel	8×8	Knights capture like bishops; bishops capture like knights
horde	8×8	White: full army vs Black: 36 pawns
immunizationChess	8×8	Captures grant adjacent enemies temporary immunity
janus	8×10	Two Januses (B+N) on a 10-wide board
khans-chess	8×8	Asymmetric: FIDE vs Mongol Horde with divergent movers
kingOfTheHill	8×8	King reaching d4/d5/e4/e5 wins instantly
knightmate	8×8	Knight is royal; Kings move as knights
leganChess	8×8	Berolina pawns; King and Queen swap squares
los-alamos	6×6	First computer chess (1956); no Bishops
madrasiChess	8×8	Same-type opposing pieces paralyse each other
maharaja	8×8	One Amazon (Q+N) vs a full army
makpong	8×8	King cannot move out of check; must block or capture
makruk	8×8	Thai chess; Khon moves 5 directions, rank-6 promotion
marseillais	8×8	Two moves per turn (except White's first)
mccooey	hex	91-hex board; diagonal pawn captures, stalemate draws
medusaChess	8×8	Queen petrifies attacked enemies for 2 turns
mini-hexchess	hex	37-hex board; no Queen piece
minichess	5×5	Gardner's 5×5 with all piece types
monsterChess	8×8	White moves twice but starts with only K, R, pawns
nightrider	8×8	Knights replaced by Nightriders (chained knight-leaps)
no-castling	8×8	Standard chess without castling
noRetreat	8×8	Pieces cannot move toward their own starting rank
oblong-chess	16×4	Historical 4×16 board; Shatranj pieces
omnicide	8×8	Lose all pieces to win; captures NOT forced
orda-chess	8×8	Asymmetric: standard vs Horde with divergent movers
orda-mirror	8×8	Both players use the Horde army
ouk-chaktrang	8×8	Cambodian chess; King may leap as Knight on first move
patrolChess	8×8	Can only capture when defended by a friendly piece
pawns-only	8×8	Kings and pawns only; first to promote wins
peasants-revolt	8×8	White: K+8P vs Black: K+2N+8P
petty	5×6	All piece types on 5×6; single copies
poisonChess	8×8	Capture squares become poisoned for 3 turns
progressive	8×8	Moves escalate: 1, 2, 3, 4... Check ends turn early
progressive-italian	8×8	Progressive; no check until final move of turn
racingKings	8×8	No checks; race your King to rank 8
recruitmentChess	8×8	Captured piece defects to vacated square
rifle	8×8	Capturing piece stays on its square
shafran	hex	70-hex board with 9 files; castling permitted
shatar	8×8	Mongolian chess; mate must include shak; bare king draws
shatranj	8×8	Medieval Islamic chess; bare king and stalemate win
shatranj-kamil	10×10	10×10 Arabic variant with War Machines
singleCheck	8×8	One check wins
sittuyin	8×8	Burmese chess; placement opening phase
stalemate-wins	8×8	Stalemate is a win instead of a draw
suicideChess	8×8	Forced captures; stalemate is a draw
teleportChess	8×8	3 teleports per game; move any piece to any empty square
threeCheck	8×8	Three checks wins
toroidal-byzantine	4×16	Circular board with radial wraparound
toroidal-chess	8×8	All four edges wrap (torus topology)
torpedo	8×8	Pawns can double-step from any rank
turkish-great-chess-iii	12×12	Ottoman 12×12 with multiple rook-type pieces
turkish-great-chess-iv	14×14	14×14 with mixed Indian/Persian piece names
upside-down	8×8	Pieces start on the opponent's back rank
weakChess	8×8	Weakest piece type must move first
wildebeest	10×11	Camels and Wildebeests (N+Camel) on 11×10

AI difficulties

Level	Depth	Notes
beginner	1	Random with basic blunder avoidance
easy	2	Simple evaluation, no deep tactics
medium	3	Full evaluation, opening book, captures extended
hard	4	Transposition table, quiescence search
expert	5+	Full search with iterative deepening

Puzzle API

1,557 puzzles available as static JSON at /api/puzzles/index.json.

// Fetch puzzle data
const res = await fetch('https://engine.moddable.games/api/puzzles/index.json')
const data = await res.json()

// data.standard = [{ id, fen, solution, rating, themes }]
// data.variants = [{ id, variant, fen, solution, rating }]
// data.meta = { count: 1557, standard: 606, variants: 951 }