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Polyglot is a node module to search moves in polyglot format opening books. For a description of the polyglot book format refer to this link.


Make sure you have node.js installed. Then do:

$ npm install polyglot-chess


var Polyglot = require('polyglot-chess');
var obj = new Polyglot();
var fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
console.log("Polyglot hash for fen " + fen + " is: " + obj.hash(fen));
console.log("Best move in the book is: " + obj.find(fen, "book.bin", true));
console.log("Random move in the book is: " + obj.find(fen, "book.bin", false));



Polyglot exposes following functions -

find(fen, bookFile, findBest)

find takes a fen string and a book file path and looks up the hash in the book file. If findBest is true it returns the best move according to the weight otherwise it returns a random move with the given hash. The chance of a random move being returned is in proportion to its weight. If no move is found it returns an empty string.


hash takes a fen string and returns its polyglot hash.


To lint the js files with jshint run the command:

$ grunt lint

Running Tests

To run the tests with mocha run the command:

$ grunt test


Fork, pick an issue to fix from issues or add a missing feature and send a pull request.


This work is derivative of the excellent stockfish polyglot book source code.


Polyglot is released under the MIT License. See the bundled LICENSE file for details.