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OliThink - Oldie Goldie

A chess engine with more than a quarter-century of history. Its origins date back to the 1990s. Unusual, with almost no chess knowledge, playing with a strength of 3025 Elo!

OliThink is a free open source chess engine by Oliver Brausch, written with C and Java versions available; license: MIT.

Looking from a programmer's point of view, almost all chess engines are written in a similar way: they contain from several to dozens of files which results in thousands - tens of thousands of lines of source code and a huge number of functions, procedures, subroutines, etc. In short: they are complex programming creations.

OliThink consists of... a single file, which contains within it all the source code needed to build the engine. It is an incredibly fast chess engine capable of counting hundreds of millions (!) of moves in just one second.

Quoting the author:


One of the main aims was to create a strong engine with minimalistic and clear code. OliThink has no chess knowledge except mobility. The size of the source code has never exceeded 50kByte. Everything in the code is unique, there is no copy of other engines.


Source: GitHub

This small in size but powerful in strength OliThink is so well written by Mr. Oliver Brausch that it can easily be compiled under probably any architecture that supports C or Java, allowing fans of different operating systems to enjoy this chess engine.


Complete rewrite of OliThink with a very fast move generator (based on OliPerft). Engine runs without any chess information. No pawnstructure, no tables etc.


Source: OliThink home page.

In the MCERL competition (ongoing), the latest version of OliThink-5.10.1 playing on a fast MacBook Pro with an Apple Silicon CPU reached a strength of 3025 Elo.

According to the CCRL rating list, the previous version of OliThink-5.9.7 received 2868 Elo.

Source: CCRL

Below are examples from two games in which OliThink has faced other engines playing at levels higher than 3000 Elo.

White has Avalanche, which is the first and strongest chess engine written in the Zig programming language.

For the price of one Pawn, OliThink has gained a promising position in which it has the initiative.

Avalanche plays the innocuous 17.c3?? with the goal of reinforcing the white Pawn standing on the d4 field, which is attacked by the black Queen and Knight.

Unfortunately, this is a dramatic miscalculation when the opponent is such a fast counting engine as OliThink.

Black with the help of only a few forcing moves plunges white. After playing the black Rook and expelling the white Queen, there is a beautiful move by the black Knight to the h4 field, 18...Nfh4!

If the white Queen moves away, the game ends with the white King's mate. Avalanche accepts the sacrifice of the black Knight. Events are moving quickly. After only 21 moves, OliThink achieves a decisive advantage. Avalanche put up hopeless resistance for several more moves.

A short and nice game in which OliThink showed his tactical skills.

Downloadable game in PGN format.

Avalanche 1.2.0 vs OliThink 5.10.1
Download ZIP • 1KB

In the next game, OliThink's opponent is chess engine Winter, a demanding and relentless player with a strength of 3147 Elo.

This game is somewhat similar to the one previously discussed, as black sacrificed Pawn to gain initiative and attack. And this time it was accomplished by Winter. Let's see how OliThink dealt with Winter's massed downright frenzied attack.

Winter played 21...Bh4? attacking the white King's position putting pressure on the white Pawn on the f2 square, which is weak at this moment.

OliThink strengthens the white king's defense and brings the Queen into his vicinity.

Winter introduces a second black Bishop into the scene, however, the whites remain calm and play according to a precise defense plan.