|Initial release||May 15, 2010|
|Stable release||4 / November 25, 2013|
|Operating system||Microsoft Windows|
Houdini is a UCI chess engine developed by Belgian programmer Robert Houdart. It is influenced by open source engines IPPOLIT/RobboLito, Stockfish, and Crafty. Earlier versions are free for non-commercial use (up to version 1.5a), but later versions (2.0 and onwards) are commercial. As of October 2015, Houdini 4 is the third top-rated chess engines on major chess engine rating lists after Stockfish and Komodo.
Chess commentator and video annotator CM Tryfon Gavriel compared Houdini's playing style to that of the Romantic Era of chess, where an attacking, sacrificial style was predominant.
|1.0||May 15, 2010||First release|
|1.01||June 1, 2010||Bug fixes, improved search algorithm|
|1.02||June 18, 2010||SMP and hash collision bug fixes. Work-around for Shredder GUI.|
|1.03||July 15, 2010||Multi-PV, searchmove and large page support. Improved evaluation function.|
|1.03a||July 17, 2010||Bug fix for Multi-PV|
|1.5||December 15, 2010||Improved search and evaluation. Gaviota Table Base Support.|
|1.5a||January 15, 2011||Maintenance update with work-arounds for Fritz GUI and other minor improvements.|
|2.0||September 1, 2011||First commercial release. Improved analysis capabilities, enhanced search and evaluation. Houdini Pro version for high-end users with powerful hardware (multi-core support). Chess960 support. Strength limit feature. Position learning. Save hash to file, load hash from file, never clear hash.|
|2.0b||November 7, 2011||Maintenance update with minor bug corrections and Nalimov EGTB support.|
|2.0c||November 20, 2011||Maintenance update with minor bug corrections and new analysis options. MultiPV_cp option to limit multi-PV analysis to moves within a range of the best move. FiftyMoveDistance option to make the 50-move rule kick in earlier. UCI_elo and UCI_limitStrength options as UCI standard-compliant alternative to Strength option. Exit on detection with GUI exit.|
|3.0||October 15, 2012||Major new version. Improved search and evaluation (+50 Elo), Tactical Mode, Scorpio bitbases, accelerated Principal Variation Search "Smart Fail-High", optimized hash usage.|
November 25, 2013
|Major new version. Improved search and evaluation (+50 Elo), 6-men Syzygy table bases (coding provided by Ronald de Man)|
The latest stable release of Houdini comes in two versions: Houdini 4 Standard and Houdini 4 Pro. Houdini 4 Pro supports up to 32 processor cores, 256 GB of RAM (hash) and is NUMA-aware, Houdini 4 Standard only supports up to six processor cores, 4GB of hash and is not NUMA-aware. As with many other UCI engines, Houdini comes with no GUI, so a chess GUI is needed for running the engine. Houdini 4 uses calibrated evaluations in which engine scores correlate directly with the win expectancy in the position.
Robert Houdart describes his engine as original and admits taking ideas from the open source programs IPPOLIT/Robbolito, Stockfish and Crafty. However, some chess programmers raised suspicions that Houdart may have taken ideas from the controversial Ippolit/Robbolito source-code "too literally" as the initial base of his program.
Houdini has won top honors in the TCEC tournament, which is often regarded as the Unofficial World Computer Chess Championship. Houdini has won three seasons to date, and narrowly failed to qualify for the finals in nTCEC Season 2, having lost out to Komodo and Stockfish.