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Home * Engines * Houdini

a chess engine by Robert Houdart, which appeared in 2010 as closed source engine, free for non-commercial use. In January 2011, Houdini 1.5 was leading Ingo Bauer's IPON rating list [2]. Houdini 2, released in September 2011, is commercial and bundled with a number of ChessOK products, such as Aquarium, Chess Assistant [3], and since December 2011, Chess King [4]. Houdini 1.5a remains available as a free download [5]. Houdini 3, released in October 2012, has further improved by more than 50 Elo points [6]. According to its author, Houdini 3 applies a accelerated principal variation search, also dubbed "Smart" Fail-High. If a different move becomes best at very high search depths at the root, re-searches to determine its exact score and the new principal variation are done faster due to a reduced search depth, presumably in conjunction with extensions along the PV [7]. Since November 2012, Houdini 3 is available as ChessBase engine [8] . Houdini 4, released in November 2013, was about 50 Elo stronger than its predecessor, and features 6-men Syzygy bases.

Houdini 5

Released about three years after the previous version, in November 2016, Houdini 5 is vastly improved being about 200 Elo stronger than Houdini 4. It has a completely rewritten evaluation with more aggressive king safety and sophisticated piece mobility, features a more selective search, exploring critical variations significantly deeper, and for hardware with multiple processors, Lazy SMP. Houdini 5 Pro supports up to 128 threads, up to 128 GiB of hash memory, large memory pages, NUMA-architecture, and Nalimov tablebases to find the shortest path to mate.

A development version of Houdini 5 qualified for TCEC Season 9 Superfinal, and even won the TCEC Season 9 Rapid tournament. The final release version of Houdini 5 is about 30 Elo stronger than the engine that played in the TCEC tournament so far. But that was apparently not enough for Stockfish 8 in long time control matches - Houdini 5 lost the 100 game Superfinal with 45½ - 54½.

Houdini 6

Released in September 2017, Houdini 6 again improved in search and evaluation to add another 50-60 Elo in strength, which roughly corresponds to doubling the computational power of the computer [9]. Houdini 6.03 won the TCEC Season 10 Superfinal versus Komodo 1970.00, a successor of Komodo 11, with 53 - 47 (+15=76-9) [10] [11].

Houdini's Origin

Robert Houdart claims his engine is original [12], and admits taking ideas from the open source programs Ippolit/Robbolito, Stockfish and Crafty [13] . Other programmers and forum members raised suspicions that Robert took ideas from the controversial Ippolit/Robbolito source code too literally as initial base of his program [14] [15] [16] [17].

Sources of Inspiration

Robert Houdart on the origins of Houdini in CCC, June 08, 2010 [18]

From the start I have very clearly acknowledged the different sources of inspiration for Houdini (Ippo/Robbo, Stockfish and Crafty) and have shown every respect for the hard work of others, be it on my web site, in the readme file, or in this forum ...
Houdini and the Ippo family have lots of high-level similarities, but zillions of low-level subtle differences.

Claims have been made that I "just changed a couple of resource strings", "made a cheap compile" or "grabbed some free code", but, in truth, none of you have any clue about the effort that was invested in Houdini.
It is funny that I would not be called a "real" chess engine author, when I am both a professional software developer and a reasonably strong chess player (peak 2280 rating), who has been writing chess engines for over 25 years now in a variety of programming languages.
It is sad that on the one hand you request that everybody demonstrates respect for the hard work of others, but on the other hand you seem to be unable to extend the same courtesy (or even the benefit of the doubt) to Houdini. 

Material Table

The idea to index the material table in the same manner as Robbolito, with combined counters of queens, rooks, light and dark bishops, knights and pawns, and to calculate piece counters from that table-index by a sequence of mod/div operations by {2,2,3,3,2,2,2,2,3,3,9,9} might be considered obvious after studying the mentioned source code, and if applying that scheme, there is hardly anything to avoid a sequence of almost identical x86 machine code with same constants for reciprocal multiplication [19].

Strelka 5

Robert Houdart on Strelka 5, December 04, 2011 [20]

Strelka 5 is Houdini 1.5 RE, not Houdini 2. I share your fears, any #1 engine will be RE'd in a matter of months. For Houdini 1.5 it's taken about 6 months. 

Reply by Richard Vida [21]

You mean 6 months until Strelka has been released to public. You do not know how much time did Yuri Osipov spent on RE, neither when he did start his RE project. For me it took barely one week. As Milos S. pointed out [22] , you made RE very very easy because of starting your project from Robbolito codebase... Personally I see no problem with that (other than you not telling the truth). 


In March 2020, an anonymous poster who came into possession of Houdini 6's source code, apparently due to access to a subversion server owned by Robert Houdart, claimed Houdini 5 and 6 were Stockfish derivatives [23] [24]. In summer 2021, the Stockfish team filed a lawsuit against ChessBase to enforce the consequences of the license termination concerning Fat Fritz 2 and the allegedly Stockfish derivative Houdini 6 sold by ChessBase [25] [26] [27].

Release Dates

  • Houdini 1.0 : May 15, 2010
  • Houdini 1.5 : December 15, 2010
  • Houdini 2.0 : September 01, 2011
  • Houdini 3 : October 15, 2012
  • Houdini 4 : November 25, 2013
  • Houdini 5: November 09, 2016
  • Houdini 6: September 17, 2017


Chess Engine

Harry Houdini

Harry Houdini (2007). The Right Way to Do Wrong. Librivox audio recording from the Internet Archive


2010 ...


Re: Houdini with 1:1 Robbolito-code? by Norman Schmidt, CCC, October 12, 2011




2015 ...




2020 ...

External Links

Chess Engine




Rating Lists

Harry Houdini


  1. The Grim Game a 1919 silent film starring Harry Houdini
  2. IPON-Rating-List Archive 2009/2010/2011 by Ingo Bauer
  3. Houdini 2 Aquarium products family has been released!, ChessOK, October 07, 2011
  4. Chess King Released, ChessOK, December 14, 2011
  5. Re: Houdini 2 is released by Robert Houdart, CCC, September 02, 2011
  6. IPON-Rating-List, 2012.10.17 by Ingo Bauer
  7. Re: Houdini 3 reducing the depth feature by Robert Houdart, CCC, October 19, 2012
  8. Houdini 3 Standard multiprocessor version, ChessBase Shop
  9. Houdini Chess Engine
  10. Houdini is TCEC Season 10 champion!, Chessdom, December 07, 2017
  11. Interview with Robert Houdart, author of the champion engine Houdini, Chessdom, December 08, 2017
  12. Re: Why Is Houdini Not Entered In The WCCC?? by Robert Houdart, Open Chess Forum, August 04, 2010
  13. Houdini Chess Engine - Acknowledgements
  14. Re: Why Is Houdini Not Entered In The WCCC?? by kingliveson, Open Chess Forum, August 09, 2010
  15. Re: Why Is Houdini Not Entered In The WCCC?? by Robert Houdart, Open Chess Forum, August 10, 2010
  16. Re: Computer Chess Biggest Liar by kingliveson, OpenChess Forum, October 11, 2011
  17. Re: Interesting poll by Rebel, Rybka Forum, July 15, 2012
  18. Re: Purpose of Chess Engine Origins forum is...? by Robert Houdart, CCC (Computer Chess Club: Engine Origins, requires registration), June 08, 2010 in a reply to Jeremy Bernstein
  19. Houdini - a cheap compile of Ippo/Robo by Lance Perkins, CCC - Computer Chess Club: Engine Origins, May 29, 2010 (requires login)
  20. Re: Komodo 4 on long time control by Robert Houdart, CCC, December 04, 2011
  21. Re: Komodo 4 on long time control by Richard Vida, CCC, December 04, 2011
  22. Re: Lazy eval - test results by Milos Stanisavljevic, CCC, December 01, 2011
  23. Houdini is a Stockfish Derivative (and started life as a Robbolito derivative) by cucumber, CCC (Engine Origins requires registration), March 22, 2020
  24. Houdini is a clone of Stockfish 8 by c9publice...@gmail.com, FishCooking, March 26, 2020
  25. Our lawsuit against ChessBase, The Stockfish team, Stockfish Blog, July 20, 2021
  26. Re: Stockfish: Our lawsuit against ChessBase by Andrew Grant, CCC, July 24, 2021
  27. GitHub - crossopterygian/Houdini_6: uci chess engine
  28. Part 1 covers Houdini, Rybka, Komodo, Stockfish, Critter, Naum, Chiron and Spike
  29. Ply versus ELO by Greg, HIARCS Forum, May 30, 2020 » Diogo R. Ferreira - Impact of the Search Depth ...
  30. Jean Eugène Robert-Houdin - Wikipedia
  31. Arpad Elo - Wikipedia
  32. Houdini 5 to participate in TCEC Season 9, Chessdom, April 13, 2016

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