Zach's Chess Test (ZCT)

This is the internet home for ZCT, a chess engine written by Zach Wegner. ZCT technically stands for Zach's Chess Test, but that sounds stupid, so it's just called ZCT. You can reach me (Zach) through email at zwegner at gmail dot com.

I also post on CCC: and the Winboard Forum:

I also act as an organizer at the Chess Programming Wiki:
It's pretty cool, and you can learn a lot there. There's even a page for ZCT!


The chess program known as Zach's Chess Test has been in existence since around 2003. I created various engines around the time period of 2002-2003. After a hard drive crash, a new source base was created. The idea was to create a good chess engine using bitboards. Though this program served as the basis for much of my chess programming development as well as new ideas, the project eventually dwindled into weakness, bugginess, and unintended obfuscation of code. The old code base was abandoned between 2005 and 2006, and currently resides in an unreachable state on an old hard drive... Good riddance, I say.

A New Beginning

An entirely new engine was created on June 1, 2005. This code base has been designated ZCT 0.3.x. The latest release is v0.3.2451, released on July 12, 2008. The engine was released to the public, with source under the Gnu GPL, on April 29, 2008. The engine has been in more or less continous development since then.


ZCT is an unrotated bitboard searcher that is characterized by heavy use of null move pruning and LMR, which is offset by a relatively heavy-weight quiescence search. The eval is pretty lousy at the moment.

ZCT is built in pure C, though an assembler lock is used for SMP on some platforms. ZCT is (in my extremely biased opinion) one of the most readable chess programs in existence, and definitely one of the most well-commented. I always appreciate any feedback on the source code, good or bad.

ZCT can use multiple processors. It uses the DTS algorithm, formulated by the Cray Blitz team. ZCT is the only open source DTS implementation, and one of the very few implementations period. You can read Bob Hyatt's DTS paper here:

Getting ZCT


To submit a bug report for ZCT, go to the SF bug tracker:

ZCT has a mailing list, You can subscribe here:

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