♟️ ChessKit

A Swift package for efficiently implementing chess logic.

For a related Swift package that contains chess engines such as Stockfish, see chesskit-engine.

Usage

1. Add chesskit-swift as a dependency

   • In an app built in Xcode,
   • or as a dependency to another Swift Package.

2. Next, import ChessKit to use it in Swift code:

import ChessKit

// ...

Features

• Representation of chess elements
  • Piece: represents a single piece on the board, given by its color, type, and location on the board
  • Square: represents a square on the board
  • Move: represents a piece move, along with other metadata such as captures, annotations, and disambiguations
  • Position: represents a single position on the chess board
  • Board: validate and make moves in accordance with chess rules
  • Game: manage positions throughout a game and PGN tags
  • Special moves (castling, en passant): handled automatically by Position and Board
• Move validation
  • Implemented using highly performant UInt64 bitboards.
• Move branching and variations
  • Implemented using a performant tree-like data structure MoveTree.
• Pawn promotion handling
• Game states (check, stalemate, checkmate, draws)
• Chess notation string parsing
  • PGNParser
  • FENParser
  • SANParser
  • EngineLANParser (for use with UCI engines)

Examples

• Create a board with the standard starting position:

let board = Board()

• Create a board with a custom starting position using FEN:

if let position = Position(fen: "rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2") {
    let board = Board(position: position)
    print(board)
}

// 8 ♜ ♞ ♝ ♛ ♚ ♝ ♞ ♜
// 7 ♟ ♟ · ♟ ♟ ♟ ♟ ♟
// 6 · · · · · · · ·
// 5 · · ♟ · · · · ·
// 4 · · · · ♙ · · ·
// 3 · · · · · ♘ · ·
// 2 ♙ ♙ ♙ ♙ · ♙ ♙ ♙
// 1 ♖ ♘ ♗ ♕ ♔ ♗ · ♖
//   a b c d e f g h
//
// (see `ChessKitConfiguration` for printing options)

• Move pieces on the board

let board = Board()
// 8 ♜ ♞ ♝ ♛ ♚ ♝ ♞ ♜
// 7 ♟ ♟ ♟ ♟ ♟ ♟ ♟ ♟
// 6 · · · · · · · ·
// 5 · · · · · · · ·
// 4 · · · · · · · ·
// 3 · · · · · · · ·
// 2 ♙ ♙ ♙ ♙ ♙ ♙ ♙ ♙
// 1 ♖ ♘ ♗ ♕ ♔ ♗ ♘ ♖
//   a b c d e f g h

// move pawn at e2 to e4
board.move(pieceAt: .e2, to: .e4)
// 8 ♜ ♞ ♝ ♛ ♚ ♝ ♞ ♜
// 7 ♟ ♟ ♟ ♟ ♟ ♟ ♟ ♟
// 6 · · · · · · · ·
// 5 · · · · · · · ·
// 4 · · · · ♙ · · ·
// 3 · · · · · · · ·
// 2 ♙ ♙ ♙ ♙ · ♙ ♙ ♙
// 1 ♖ ♘ ♗ ♕ ♔ ♗ ♘ ♖
//   a b c d e f g h

• Check move legality

let board = Board()
print(board.canMove(pieceAt: .a1, to: .a8)) // false

• Check legal moves

let board = Board()
print(board.legalMoves(forPieceAt: .e2))    // [.e3, .e4]

• Parse FEN into a Position object, PGN (into Game), or SAN (into Move).

// parse FEN using Position initializer
let fen = "rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2"
let position = Position(fen: fen)

// convert Position to FEN string
let fenString = position.fen

// parse PGN using Game initializer
let game = Game(pgn: "1. e4 e5 2. Nf3")

// convert Game to PGN string
let pgnString = game.pgn

// parse the move text "e4" from the starting position
let move = Move(san: "e4", in: .standard)

// convert Move to SAN string
let sanString = move.san

Command Line

The ChessKit command line interface (chesskit-cli) can be used to explore and test ChessKit features.

The interface can be accessed by running swift run chesskit-cli from the project directory. The available commands will be displayed on screen and can be used to manipulate the board.

License

ChessKit is distributed under the MIT License.