EXchess - Oldie Goldie

Darius
Nov 11, 2022
3 min read

Updated: Dec 12, 2023

Chess engine developed for more than 20 years!

In its time, it was one of the most interesting chess engines using advanced search algorithms. He played against the best and won against the best.

Interesting style of play, characterized by consistency and tough defense, more of a strategist than a tactician taking advantage of his opponent's stumbles to gain a better position/initiative and turn it into a win.

EXchess is open source chess engine by Daniel Homan, written in C++, released under the GNU Public License.

Playing power between 2900 Elo (1 CPU) and 3000 Elo (4-CPU), which means that even today it can be used to analyze human chess games at a pretty good level.

Source: CCRL

The last version was released in 2017. Today somewhat forgotten, and not rightly so. With this post I'd like to refresh a bit the memory of EXchess, an unexceptional chess engine, which is worth running sometimes to enjoy its gameplay again. I have also collected EXchess compilations for several platforms, adding self-compiled versions for modern Macs.

Below is an example of EXchess' style of play and its effectiveness.

Crafty with white, the legendary chess engine by Professor Dr. Robert Hyatt, in its latest and most powerful version. EXchess with black.

Let's look at the placement of the pieces on the chessboard.

* Fen: 4r1rk/2qb1ppn/3p1b2/1p1P3P/2p1P3/PpP1B1R1/1P4QN/1B4RK w - - 5 34

Dream position for Crafty, who has worked out great attacking possibilities: heavy figures on the g-line, Bishops looking directly at the black King's position, just a move with a pawn to the e5 field to completely open the positions, the black Queen away from his King with no possibility of a quick defense.

In this position, Crafty played 34.Bh6? Unfortunately, this move is not a good one.

The best continuations would have been created after playing 34.Bd4 or 34.Nf3. Even the immediate 34.e5 led to a better game for white.

EXchess exploits Crafty's mistake by playing the unexpected 34...Bh3!

This move, which is not easy to find, disorganizes white's assault on the black king's position. EXchess equalizes the game with one move, though. Crafty doesn't realize it yet.

After several exchanges, EXchess plays 37...Be5 an important move from a strategic point of view, which in practice takes the white Bishop out of the game.

A few more moves and another "quiet" success for EXchess, which further reduced the material on the chessboard. This is to his advantage, because Crafty, although in possession of the white Bishop, is stuck on the b1 square.

Crafty feels confident enough to even allow the exchange of Queens.

EXchess understands the positions on the chessboard perfectly. Each successive exchange and reduction of material increases it chances more and more due to the excluded white Bishop still standing on the B1 field.

41.Nxe5??

Blunder that will cost Crafty a loss in this game.

"The dust has settled". EXchess after disorganizing white's attack, blocking Bishop on B1 and favorable reduction of material - has a completely winning position.

Crafty is still trying desperately to turn the game around, but they are already doomed to failure.

Downloadable game in PGN format

A great game without spectacular sacrifices for the fact that it contained interesting startegies from both sides!

In the first phase of the game, Crafty strenuously built up its lead despite the lack of clear blunders on Exchess' part. And then, making his 34th move, Crafty played a seemingly winning move. 34.Bh6 would have been excellent, had it not been for EXchess' magnificent counter move of the black goon 34...Bh3!

After that, things moved quickly. It only took 7 consecutive moves for Exchess, taking advantage of Crafty's blunder and his wrong strategic decisions, to lead to a complete collapse of white's position.