Syzygy Bases

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Home * Knowledge * Endgame Tablebases * Syzygy Bases

Syzygy - Three Planets Dance Over La Silla [1]

Syzygy Bases, [2]
a compact six piece endgame database developed by Ronald de Man, published on April 01, 2013. Since August 2018, seven piece Syzygy Bases are available after an effort by Bojun Guo started in March 2018 [3]. The generator is released under the GNU General Public License Version 2, the thread safe probing code is released without restrictions [4] .


File Types

Syzygy Bases consist of two sets of files, WDL files (extension .rtbw) storing win/draw/loss information considering the fifty-move rule for access during search, and DTZ files (extension .rtbz) with distance-to-zero information for access at the root. WDL has full data for two sides but DTZ50 omitted data of one side to save space. Each endgame has a pair of those types.

File Sizes

Men WDL DTZ Total
3-5 378.1 MiB 561.9 MiB 939.0 MiB
6 67.8 GiB 81.4 GiB 149.2 GiB
7 8.5 TiB 8.3 TiB 16.7 TiB


Syzygy EGTB is significantly smaller than any existent DTM EGTB. It is 7 times as small as Gaviota for 5 men, 8 times as small as Nalimov for 6 men, 8 times as small as Lomonosov for 7 men. However, when all DTM EGTBs have full data of two sides, Syzygy EGTB omits data of one side for DTZ data to save space. Ronald de Man estimated if keep them all, the Syzygy's 6 men size may increase 158 GB, become 307 GB in total, double on size, be 4 times as small as Nalimov 6 men.


Up to 6-man

On the first release (Apr 01, 2013) the generator was ready to generate all endgames up to 6 men. It is multithreading and processes completely in RAM. To generate all 6 men, it requires a system with at least 32 GB of RAM and may run in 5 days (the period was measured with a computer 6-core i3930K @ 4.2Ghz, 64 GB).


Ronald de Man wasn't initially interested in the creation of 7-men Syzygy Based [5] since the generation would require about 1 TB of RAM, too expensive at that time. Generation time would be about 64 x per table, which means around 175 x time total [6].His original generator could not create them. But in 2018, he supported Bojun Guo in his 5-month attempt to generated them [7]. His hardware was estimated at over US$ 90K. In August of 2018 their creation was completed [8][9].


After the completion of 7-man, many people start being curious about the feasibleness of building 8-man. Ronald de Man made an estimation that task requires computers with 64 TB RAM and 2000 TB hard disks[10] (costed about $640K and $40K respectively in 2020 [11]).


Syzygy endgame files may contain 128-bit checksum keys at the end of those files. It also has its own code for checksums (based on Google's cityhash library).


During the Search

During the search, with the WDL tables stored on SSD [12] , it is possible to probe the tables at all depths without much slowdown. They have been tested in Ronald de Man's engine Sjaak (playing on FICS as TrojanKnight(C)) a couple of months quite successfully, don't probing in quiescence search.

At the Root

At the root, since pure DTZ50-optimal play (i.e. minimaxing the number of moves to the next capture or pawn move by either side) can be very unnatural, it might be desirable to let the engine search on the winning moves until it becomes clear that insufficient progress is being made and only then switch to DTZ-optimal play (e.g. by detecting repetitions and monitoring the halfmove clock) [13].

Pros & Cons


  • Small sizes. It is about 8 times as small as the second-best EGTBs. Having small sizes is the main success key of Syzygy Bases since it is much easier to create, store, provide, download than other EGTBs
  • Free and more popular (than other EGTBs) to find on the Internet
  • Support DTZ50 metric. That metric can help engines to have better results than DTM which is supported widely by other EGTBs


  • Hard to integrate with chess engines. Ronald de Man has not provided probing code as an independent library but as a part of Stockfish chess engines. The probe code has integrated too deeply with that chess engine code and it requires a lot of effort to de-integrate, modify and integrate with other chess projects
  • Hard to understand and contribute to the project. ETGB itself is a hard topic. Syzygy EGTB has also integrated with many advanced techniques/tricks. It is written in old-style C language. All make it become very hard to understand and/or modify to improve or for other purposes
  • DTZ50 metric may lead the engines to win in much longer and ugly ways, compared with DTM one

Data publish

Ronald de Man has provided only open source code for generators/probers but not endgame files themselves. Using his tools some people have generated endgames and published them via DVD or online.


As of February 2015, all 3-5 and most important 6-men Syzygy Bases are commercially available on 4 DVDs by ChessBase as Endgame Turbo 4 for their products Deep Fritz 14, Komodo Chess 8, Houdini 4 or ChessBase 12/13 [14] [15].

Free Download

There are some free FTP servers for downloading such as Bojun Guo and Lichess servers.

3-6 men

The sizes of those men are small enough to download and store on modern computers. Users should download them in full sets (3, 4, 5, 6 men).

7 men

All 7 men files' size is over 16.7 TiB, over storages of typical modern computers. They also require a long time to download too. Thus some users choose to download one or a few endgames only, based on their statistics of use in endgames. Bellow is the top 20 of those endgames by their order. The first one, KRPPvKRP, has a significantly higher frequency of use than the others and should be always downloaded:

Rank Name Rank Name Rank Name Rank Name

Probe Code and Tools


Ronald de Man did not provide the probe code as an independent library. Instead, he published it firstly as an already integrated code for Stockfish chess engines. It is c++ code and it has been rewritten, updated several times by Stockfish team.


Fathom is a stand-alone Syzygy based probing tool and API by Basil Falcinelli, introduced in November 2015 along with his Gull 3 release [16] . Unlike the original tbprobe code, Fathom does not necessarily require the callee to provide move generation functionality. The new modifications and extensions to Ronald de Man's original code which can be "redistributed and/or modified without restrictions", are released under the permissive MIT License. The API consists of three functions [17] :

  • tb_init initializes the tablebase
  • tb_probe_wdl probes the Win-Draw-Loss (WDL) table for a given position
  • tb_probe_root probes the Distance-To-Zero (DTZ) table for the given position.

Jon Dart has a fork of Fathom with some bug fixes and enhancements [18], also supporting 7-man [19].


Pyrrhic is a cleaned up Fathom by Andrew Grant, introduced in August 2020 [20] [21].

Elo gained by Stockfish

Stockfish with Classical Evaluation

Fishtest team revealed a test with Stockfish (SF10dev) at 10+0.1, with all Syzygy WDL files on RAM, testing using none(0), 4, 5, and 6 men TB in a round-robin tournament[22].

Rank Name Elo +/- Games Score Draws
1 syzygy6 13 2 82591 51.8% 59.5%
2 syzygy5 2 2 82590 50.3% 59.4%
3 syzygy4 -7 2 82591 49.0% 59.3%
4 syzygy0 -7 2 82592 48.9% 59.4%

Stockfish NNUE

Elo gains by Stockfish NNUE with Sygyzy 6 men are clearly decreased[23]. With version 15, it gains only 2.7 Elo.



by Ronald de Man in a reply to Guy Haworth, April 06, 2013 [24] :

I create both WDL and DTZ in one go, so I don't use WDL in the creation of DTZ. The algorithm used is the grandfather algorithm with 2 plies per iteration (I think HGM calls this leapfrogging, but I might be wrong). I tried the outcounting method, but it didn't seem to be competitive (and it makes things more complicated). [25] [26]
A pure WDL/DTZ pair is not of much use for creating WDL50+/DTZ50+. I create tables in RAM that have all the information necessary for WDL50+ and DTZ50+, then permute them to different indexing schemes and compress. I do test runs on subsets of the data to find good permutations. (The idea to try permutations is from Jesper Torp Kristensen's master thesis.) [27] [28] 

Ronald de Man in a reply to Nguyen Pham, April 15, 2020 [29] :

Syzygy WDL is double sided, DTZ is single sided.
So to know whether a 7-piece position is winning, losing or drawn (or cursed), the engine needs to do only a single probe of a 7-piece WDL table. (It may in addition have to do some probes of 6-piece WDL tables if any direct captures are available.)
If the engine needs to know the DTZ value (which is only necessary when a TB root position has been reached), the probing code may have to do a 1-ply search to get to the "right" side of the DTZ table.
For 6-piece TBs, DTZ is 81.9GB when storing only the smaller side of each table. Storing both sides might require perhaps 240GB.

Morgan Houppin explained why his chess engine Stash doesn't have Syzygy probe code, March 25, 2021 [30] :

Syzygy probing is a hell of a mess, and I don't want to plug two thousand lines of foreign code that I don't understand, nor do I have the motivation to fully understand how Syzygy files are stored, and then write the additional two thousand lines of code to read them for a mere 5 Elo gain at TCEC.

Endgame News

In his 2014 Chess Endgame News in ICGA Journal, Vol. 37, No. 2 [31] , Guy Haworth classified Syzygy Bases as new data in three ways:

  1. 5-valued scale for evaluating positions in the context of the FIDE 50-move rule (50mr) which constrains the length of phases of play
    1. +2 ≡ unconditional win for the side to move
    2. +1 ≡ ‘win’ which can be frustrated by best play and a 50mr draw-claim
    3. _0 ≡ unconditional draw
    4. -1 ≡ ‘loss’ saved by a 50mr draw-claim
    5. -2 ≡ unconditional loss
  2. depths for ‘50mr draw’ positions with value ±1
  3. depths in symmetric, information-preserving ply ‘p’

and further gives some news about early software bugs and glitches concerning ChessBase products, and the importance of MD5 to check the EGT integrity.

See also


Forum Posts

2013 ...


2015 ...


Re: Stockfish 7 and partial 6 piece syzygy problem? by Marco Costalba, CCC, September 01, 2016



Re: 7-men Syzygy attempt by Bojun Guo, CCC, August 19, 2018


2020 ...




External Links




Online Lookup



Michael Brecker, Mike Stern, Jeff Andrews, Adam Nussbaum, Joey Calderazzo


  1. It’s a real treat for photographers and astronomers alike: our skies are currently witnessing a phenomenon known as a syzygy — when three celestial bodies (or more) nearly align themselves in the sky. When celestial bodies have similar ecliptic longitude, this event is also known as a triple near-conjunction. Of course, this is just a trick of perspective, but this doesn't make it any less spectacular. In this case, these bodies are three planets, and the only thing needed to enjoy the show is a clear view of the sky at sunset. Luckily, this is what happened for ESO photo ambassador Yuri Beletsky, who had the chance to spot this spectacular view from ESO's La Silla Observatory in northern Chile on Sunday May 26 , 2013. Above the round domes of the telescopes, three of the planets in our Solar SystemJupiter (top), Venus (lower left), and Mercury (lower right) — were revealed aftersunset, engaged in their cosmic dance. An alignment like this happens only once every several years. The last one took place in May 2011, and the next one will not be until October 2015. This celestial triangle was at its best over the last week of May, but you may still be able to catch a glimpse of the three planets as they form ever-changing arrangements during their journey across the sky - source Three Planets Dance Over La Silla | ESO, Syzygy (astronomy) from Wikipedia
  2. Re: New 6-piece tablebases by Ronald de Man, CCC, April 10, 2013
  3. Re: 7-men Syzygy attempt by Bojun Guo, CCC, August 19, 2018
  4. New 6-piece tablebases by Ronald de Man, CCC, April 01, 2013
  5. Re: 7-piece syzygy by syzygy, CCRL Discussion Board, July 03, 2014
  6. Re: Syzygy tb generator for windows by syzygy, CCRL Discussion Board, June 01, 2014
  7. 7-men Syzygy attempt by Bojun Guo, CCC, March 10, 2018
  8. Powered by Ronald de Man's Syzygy endgame tablebases, 7-piece tables generated by Bojun Guo and a public API hosted by, August 19, 2018
  9. Index of /tables/standard/7/ on lichess, August 19, 2018
  10. Re: What is the best way to obtain the 7-piece tablebases? by syzygy, CCC, June 22, 2020
  11. Re: What is the best way to obtain the 7-piece tablebases? by Dann Corbit, CCC, June 23, 2020
  12. Re: SSD and the use of Tablebases by Ronald de Man, CCC, May 08, 2013
  13. Re: New 6-piece tablebases by Ronald de Man, CCC, April 05, 2013
  14. Endgame Turbo 4 by ChessBase
  15. Syzygy Tablebases: newest, fastest, smallest by Albert Silver, ChessBase News, February 08, 2015
  16. Gull 3 Linux+Syzygy and Fathom released by Basil Falcinelli, CCC, November 20, 2015
  17. GitHub - basil00/Fathom: Syzygy TB probe tool by Basil Falcinelli
  18. jdart1/Fathom · GitHub by Jon Dart
  19. 7-man Syzygy support in Fathom by Jon Dart, CCC, April 23, 2019
  20. Pyrrhic, Fathom for Humanoids by Andrew Grant, CCC, August 16, 2020
  21. GitHub - AndyGrant/Pyrrhic: Fathom, for Humanoids
  22. Collection of useful data concerning SF
  23. Useful data · official-stockfish/Stockfish · GitHub by Joost VandeVondele, August 26, 2023
  24. Re: New 6-piece tablebase generator by syzygy, CCRL Discussion Board, April 06, 2013
  25. Retrograde tablebase methods by BB+, OpenChess Forum, November 26, 2010
  26. Leapfrog: Retrograde Analysis from Leapfrog tablebase generator by Harm Geert Muller
  27. Jesper Torp Kristensen (2005). Generation and compression of endgame tables in chess with fast random access using OBDDs. Master thesis, supervisor Peter Bro Miltersen, Aarhus University
  28. OBDD - Ordered Binary Decision Diagram from Wikipedia
  29. Re: Almost perfect DTM tablebase by Dann Corbit, CCRL Discussion Board, April 15, 2020
  30. Re: Stash has lost 2 game because of NO EGTB by Morgan Houppin, CCC, March 25, 2021
  31. Guy Haworth (2014). Chess Endgame News. ICGA Journal, Vol. 37, No. 2
  32. Found an interesting research by Kirill Kryukov, April, 12, 2013
  33. Wine (software) from Wikipedia
  34. N. Jesper Larsson, Alistair Moffat (1999). Offline Dictionary-Based Compression. DCC'99, pdf
  35. LZ4 (compression algorithm) from Wikipedia
  36. Zstandard from Wikipedia
  37. BitTorrent from Wikipedia
  38. ChessDBCN by noobpwnftw, CCC, September 09, 2019

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