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The fol­low­ing text is ex­tract­ed from Wikipedia, un­der Cre­ative Com­mons At­tri­bu­tion-Share­Alike 3.0 Li­cense. For more de­tails and ref­er­ences, please ac­cess the orig­i­nal ar­ti­cle.

Chess is a two play­er game on a chess­board, with six­teen pieces (of six types) for each play­er. Each type of chess­piece moves in a unique way. The goal of the game is to check­mate the op­po­nent’s king with in­evitable cap­ture. In ad­di­tion to win­ning, there are sev­er­al ways that a game can end in a draw.


The play­er con­trol­ling the white army is named “White” and the the play­er con­trol­ling the black pieces is named “Black”. White be­gins first and the play­ers al­ter­nate moves af­ter that. A move has to be made ev­ery turn, skip­ping isn’t al­lowed. Not even when hav­ing to move means los­ing. A game con­tin­ues un­til a king is check­mat­ed, a play­er re­signs, or a draw is de­clared. De­tails are ex­plained be­low. In ad­di­tion, if the game is be­ing played un­der a time con­strain, play­ers who ex­ceed their time lim­it lose the game.


Each chess piece has its own method of move­ment. Moves are made to va­cant squares ex­cept when cap­tur­ing an op­po­nent’s piece.

With the ex­cep­tion of any move­ment of the knight and the oc­ca­sion­al castling ma­neu­ver, pieces can­not jump over each oth­er. When a piece is cap­tured, the at­tack­ing piece re­places the en­e­my piece on its square (en pas­sant be­ing the on­ly ex­cep­tion). The cap­tured piece is then re­moved from the game and may not be re­turned to play for the re­main­der of the game. The king can be put in check, but can­not be cap­tured (see be­low).


The king can move ex­act­ly one square ei­ther hor­i­zon­tal­ly, ver­ti­cal­ly, or di­ag­o­nal­ly. On­ly once per play­er, per game, is a king al­lowed to make a spe­cial move known as castling (see be­low).


The rook moves any num­ber of va­cant squares ver­ti­cal­ly or hor­i­zon­tal­ly. It al­so is moved while castling.


The bish­op moves any num­ber of va­cant squares in any di­ag­o­nal di­rec­tion.


The queen can move any num­ber of va­cant squares ei­ther di­ag­o­nal­ly, hor­i­zon­tal­ly or ver­ti­cal­ly.


The knight moves to the near­est square not on the same rank, file, or di­ag­o­nal. In oth­er words, the knight moves two squares hor­i­zon­tal­ly then one square ver­ti­cal­ly, or one square hor­i­zon­tal­ly then two squares ver­ti­cal­ly. Its move is not blocked by oth­er pieces, it ba­si­cal­ly jumps to the new lo­ca­tion.


Pawns have the most com­plex rules of move­ment:

  • If the square in­front of a pawn is un­oc­c­cu­pied, the pawn can move for­ward one square. If it has not yet moved, each pawn has the op­tion of mov­ing two squares for­ward, giv­en both squares in front of the pawn are un­oc­cu­pied. A pawn can­not move back­wards.
  • Pawns are the on­ly pieces that cap­ture dif­fer­ent­ly from how they move. They can cap­ture an en­e­my piece on ei­ther of the two spa­ces ad­ja­cent to the space in front of them (i.e., the two squares di­ag­o­nal­ly in front of them) but can­not move to these spa­ces if they are va­cant.

The pawn is al­so in­volved in the two spe­cial moves en pas­sant and pro­mo­tion.


Castling con­sists of mov­ing the king two squares to­wards a rook, then plac­ing the rook on the oth­er side of the king, ad­ja­cent to it. Castling is on­ly al­lowed if all of the fol­low­ing con­di­tions are met:

  • The king and rook in­volved in castling have not pre­vi­ous­ly moved
  • There are no pieces be­tween the king and the rook
  • The king cur­rent­ly isn’t in check, and isn’t go­ing to be pass­ing through or end­ing up in a square that is un­der at­tack by an en­e­my piece (though the rook is per­mit­ted to be un­der at­tack and can pass over an at­tacked square)

En pas­sant

If play­er A’s pawn moves for­ward two squares and play­er B has a pawn on its fifth rank on an ad­ja­cent file, B’s pawn can cap­ture A’s pawn as if A’s pawn had on­ly moved one square. This cap­ture can on­ly be made on the im­me­di­ate­ly sub­se­quent move. For ex­am­ple: if the white pawn moves from a2 to a4, the black pawn on b4 can cap­ture it en pas­sant, end­ing up on a3.

Pawn pro­mo­tion

If a pawn ad­vances to its eighth rank, it is then pro­mot­ed to a queen, rook, bish­op, or knight of the same col­or. The choice here is at the dis­cre­tion of the con­trol­ling play­er. The choice is not lim­it­ed to pre­vi­ous­ly cap­tured pieces. Hence it is the­o­ret­i­cal­ly pos­si­ble for a play­er to have up to nine queens or up to ten rooks, bish­ops, or knights if all of their pawns are pro­mot­ed.


A king is in check when it is un­der at­tack by one or more en­e­my pieces. A piece un­able to move be­cause it would place its own king in check may still de­liv­er check to the op­pos­ing play­er.

A play­er may not make any move which places or leaves his king in check. The pos­si­ble ways to get out of check are:

  • Mov­ing the king to a square where it is not threat­ened.
  • Cap­ture the threat­en­ing piece (pos­si­bly with the king).
  • Block the check by plac­ing a piece be­tween the king and the op­po­nent’s threat­en­ing piece.

End of the game


If a play­er’s king is placed in check and there is no le­gal move that the play­er can make to es­cape check, then the king is said to be check­mat­ed. This ends the game ends and the play­er los­es. Un­like oth­er pieces, the king is nev­er ac­tu­al­ly cap­tured or re­moved from the board be­cause the check­mate ends the game.


The game ends in a draw if any of these con­di­tions oc­cur:

  • The game is au­to­mat­i­cal­ly ends in a draw if the mov­ing play­er is not in check and has no le­gal move. This sit­u­a­tion is called a stale­mate.
  • The game is im­me­di­ate­ly drawn when there is no pos­si­bil­i­ty of check­mate for ei­ther side with any se­ries of le­gal moves. This draw is of­ten due to in­suf­fi­cient pieces dur­ing the endgame: king against king, king against king and bish­op, king against king and knight or king and bish­op against king and bish­op, with both bish­ops on di­ag­o­nals of the same col­or.
  • Both play­ers agree to a draw af­ter one of the play­ers makes such an of­fer.

The play­er mov­ing may claim a draw by declar­ing that one of the fol­low­ing con­di­tions is met or by declar­ing an in­ten­tion to make a move which will bring about one of these con­di­tions:

  • Fifty-move rule: There has been no cap­ture or pawn move in the last fifty moves by each play­er.
  • Three­fold rep­e­ti­tion: The same board con­stel­la­tion has oc­curred three times in a row.

If the claim is proven to be true, the game ends in a draw.


Jocly implementation

De­vel­op­ment: Michel Gutier­rez (@_mig_)

De­vel­op­ment & Graph­ic de­sign: Jérôme Choain (@jcfrog)





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