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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 February 2019, Houdini 6 is the third highest-rated chess engine on major chess engine rating lists, behind Stockfish and Komodo.[1]

Developer(s)Robert Houdart
Initial releaseMay 15, 2010; 9 years ago (2010-05-15)
Stable release
6.03 / November 20, 2017; 21 months ago (2017-11-20)
Operating systemMicrosoft Windows
TypeChess engine


Playing styleEdit

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.[2] According to Robert Houdart, Houdini's advantage against other top engines is in its handling of piece mobility, which is why it "favors aggressive play that tries to win the game".[3]

Version historyEdit

Version Release date Features[4]
1.0 May 15, 2010 (2010-05-15) First release
1.01 June 1, 2010 (2010-06-01) Bug fixes, improved search algorithm
1.02 June 18, 2010 (2010-06-18) SMP and hash collision bug fixes. Work-around for Shredder GUI.
1.03 July 15, 2010 (2010-07-15) Multi-PV, searchmove and large page support. Improved evaluation function.
1.03a July 17, 2010 (2010-07-17) Bug fix for Multi-PV
1.5 December 15, 2010 (2010-12-15) Improved search and evaluation. Gaviota Table Base Support.
1.5a January 15, 2011 (2011-01-15) Maintenance update with work-arounds for Fritz GUI and other minor improvements.
2.0 September 1, 2011 (2011-09-01) 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 (2011-11-07) Maintenance update with minor bug corrections and Nalimov EGTB support.
2.0c November 20, 2011 (2011-11-20) 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 (2012-10-15) 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 (2013-11-25)

Major new version. Improved search and evaluation (+50 Elo), 6-men Syzygy table bases (coding provided by Ronald de Man)

November 7, 2016 (2016-11-07)

Major new version, about 200 Elo stronger. Rewritten evaluation function, deeper search.

November 15, 2016 (2016-11-15)

Maintenance update with some interface corrections and improvements.

September 15, 2017 (2017-09-15)

Major new version. Improved search and evaluation (+50-60 Elo), enhanced multi-threading.

September 24, 2017 (2017-09-24)

Maintenance update with Nalimov EGTB correction and new output option.

October 1, 2017 (2017-10-01)

Maintenance update with Polyglot book support.

November 20, 2017 (2017-11-20)

Correction for incorrect detection of stalemate in positions with white pawn capture moves.

The latest stable release of Houdini comes in two versions: Houdini 6 Standard and Houdini 6 Pro. Houdini 6 Pro supports up to 128 processor cores, 128 GB of RAM (hash) and is NUMA-aware, Houdini 5 Standard only supports up to 8 processor cores, 4 GB 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 5 uses calibrated evaluations in which engine scores correlate directly with the win expectancy in the position.[4]

Competition resultsEdit

Houdini is one of the most successful engines in the TCEC tournament, which is often regarded as the Unofficial World Computer Chess Championship, with four championship wins to date.[5]

Notable gamesEdit

"Houdini Immortal"
Rybka - Houdini
Position after the 24th move. Houdini (Black) is three pawns down but has very active pieces and White's king is exposed. White couldn't avoid losing a piece 7 moves later.


  1. ^ "CCRL 40/40". Retrieved 2 February 2019.
  2. ^ "Houdini with Black pieces in the Thoresen Chess Engines Competition. Game shows Houdini playing style from 6:23" on YouTube
  3. ^ "Interview with Robert Houdart, Mark Lefler and GM Larry Kaufman". November 23, 2017. Retrieved November 24, 2017.
  4. ^ a b Cruxis, Retrieved 16 June 2012
  5. ^ "Houdini is TCEC Season 10 champion!". 7 December 2017.
  6. ^ Video annotation by Kingscrusher on YouTube
  7. ^ Monokroussos, Dennis. "Houdini 1.5a defeats Rybka 4: 23.5-16.5". Retrieved 25 October 2013.
  8. ^ Video annotation by Kingscrusher on YouTube
  9. ^ "Free Houdini beats commercial Rybka 23.5-16.5". Chessvibes. 10 February 2010. Retrieved 25 October 2013.

External linksEdit