Computer Dice

Forum Archive : Computer Dice

Jellyfish: How to check the dice

From:   John Goodwin
Date:   27 May 1998
Subject:   Satisfying yourself that Jellyfish does not cheat

It is fairly common for someone to post a question here
(, querying the apparent good luck Jellyfish (JF)
has with its dice.

I have prepared this step by step guide for anyone who is not
convinced by the simple reassurances of those who have used and trust

Section A

This is for those of a seriously pedantic disposition

  You cannot *prove* that JF *never* manipulates the dice (at least
  not in any feasible time span).

  You cannot prove absolutely, that JF did not manipulate the dice
  for a certain game, because there is an absurdly small possibility
  that it is designed to win some specific games.

Neither of these caveats should concern anyone who does not work for
the security services of a disturbingly paranoid government

Section B

To satisfy yourself that JF has not manipulated the dice in any
particular game.

  At the end of the game you wish to examine, note down the seed and
  counter. They are to be found in the status bar, at the bottom right
  of the JF window.

  Print out the moves of the game. These can be found in the file
  GAME.GAM, in the directory from which JF is run.

  Count the total number of moves for each player, and subtract this
  from the count that you have noted.

  Start a new game, and, at some point, go to Settings|Seed, and set
  the seed and counter to the values they were at the start of the
  match you are checking.

  Continue to play. You will note that the dice that are generated are
  exactly the same as those from the match that you have printed.

You may repeat the steps from XX as many times as you like, and you
will see that no matter what the state of the board, JF always
generates the same sequence from the given seed and counter.

Section C

To satisfy yourself that JF is not using foreknowledge of the dice it
is about to generate.

  Play a game, and produce a listing of GAME.GAM.

  Check Settings|Manual Dice, so that you can feed in the dice
  throws yourself.

  Now, JF will have no way of knowing what dice are about to be

  Play the game, feeding in the dice values from the game you have

  You will see that it proceeds in exactly the same way as it did when
  JF was generating the dice.

This demonstrates that JF will play the same board, the same way,
even when it is not generating the dice, and thus can have no idea
what throws will be made.

Section D

It has been pointed out that JF could (in theory) be cheating, and
keeping a record of its activities so that if you try to catch it out
if would behave as if it was innocent of any wrong doing.

If you are *that* paranoid, then you might care to run the tests on a
different machine to that on which the initial games were played.

Make sure that you disconnect both machines from any kind of network
first (before running the initial game).

That might convince you, but some good quality psychiatric treatment
would probably be more beneficial.


Do not take the contents of section D to imply any suggestion that you
are being unreasonable in questioning JF in the first instance.

If you have never played intermediate to strong players before, and
are unaware of the solid reputation that JF has amongst the many good
players who use it regularly (and the not so good ones such as
myself), you would need to be somewhat gullible not to seek some

Did you find the information in this article useful?          

Do you have any comments you'd like to add?     


Computer Dice

Dice on backgammon servers  (Hank Youngerman, July 2001) 
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Does BG by George cheat?  (George Sutty, Nov 1995) 
Does Backgammon NJ cheat?  (Greg+, June 2010) 
Does Cybergammon cheat?  (Goto Informatique, Aug 1996) 
Does David's Backgammon cheat?  (Joseph B. Calderone, June 1998) 
Does GNU Backgammon cheat?  (Robert-Jan Veldhuizen, Nov 2002) 
Does Gammontool cheat?  (Jim Hurley, Sept 1991) 
Does Hyper-Gammon cheat?  (ZZyzx, June 1996) 
Does Jellyfish cheat?  (Fredrik Dahl, June 1997) 
Does MVP Backgammon cheat?  (Mark Betz, Oct 1996) 
Does MonteCarlo cheat?  (Matt Reklaitis, June 1998) 
Does Motif cheat?  (Rick Kiesau+, Mar 2004)  [Long message]
Does Motif cheat?  (Billie Patterson, Feb 2003) 
Does Motif cheat?  (Robert D. Johnson, Oct 1996) 
Does Snowie cheat?  (André Nicoulin, Sept 1998) 
Does TD-Gammon cheat?  (Gerry Tesauro, Feb 1997) 
Error rates with computer dice  (NoChinDeluxe+, Feb 2011) 
FIBS: Analysis of 10 million rolls  (Stephen Turner, Apr 1997)  [Recommended reading]
FIBS: Are the dice biased?  (Kit Woolsey, Oct 1996) 
FIBS: Entering from the bar  (Tom Keith+, Apr 1997) 
GamesGrid: Too many jokers?  (Gregg Cattanach, Sept 2001) 
GridGammon: Are the dice random?  (leobueno+, Sept 2011) 
Jellyfish: How to check the dice  (John Goodwin, May 1998)  [Recommended reading]
Jellyfish: Proof it doesn't cheat  (Gary Wong, July 1998) 
MSN Zone: Security flaw  (happyjuggler0, June 2004) 
Official complaint form  (Gary Wong, June 1998)  [Recommended reading]
Randomness testing  (Brett Meyer+, Dec 2010) 
Safe Harbor Games dice  (Michael Petch+, Aug 2011) 
Synopsis of "cheating" postings  (Ray Karmo, Feb 2002) 
Testing for bias  (Kit Woolsey, Jan 1995) 
The dice sure seem unfair!  (Michael Sullivan, Apr 2004) 
Too many repeated rolls?  (Stephen Turner, Mar 1994) 
Winning and losing streaks  (Daniel Murphy, Mar 1998) 

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