TCEC Openings FAQ


Q:  Why do TCEC chess games not start from the opening position?

A:  The answer is rooted on our site’s general objectives, past experience trying different play formats, and our judgment on what makes an entertaining competition and therefore a successful website.


·         Our primary goal is to provide our web audience with fair and entertaining chess competitions.


·         We believe that a champion chess program ought to be able to perform well in a wide variety of opening systems, not merely those which it favors.  This approach is different from human tournaments by design.


·         We see the traditional opening position as merely one position out of many thousands that might present a chess program with a challenge.  What distinguishes the opening position in computer chess is that it is relatively balanced, meaning it has a high probability of resulting in a draw when played by top competitors at long time controls on very strong hardware.


·         Many chess programs repeatedly play a given position the same way.  When two such programs meet, they invariably produce repetitive contests.  A recent 100-game test we ran between leading engines resulted in 88% of the games concentrating into just five ECOs.  Such outcomes frustrate the majority’s desire for entertaining chess.


·         The fact that different competitors must cope with an unpredictable and unequal set of openings adds an element of chance to the competition, mitigated by the fact that competitors play from both sides of the board.  The principal risk is that competitors will be saddled with openings that are too draw-prone or too one-sided, resulting in game-pairs that fail to differentiate the competitors on the cross-table.  Our openings team is skilled at selecting opening positions that are neither hopelessly draw-prone nor one-sided.


Q:  How are openings selected?

A:  Presently the lowest two divisions (4th and 3rd) use a 2-move opening book while the next two divisions (2nd and 1st) use a 6-move opening book, both created by Nelson Hernandez (‘CatoTheYounger_TCEC’).  Book lines from both books are selected randomly.  These book lines come from a 15 million-game database of human tournament, correspondence and high-Elo games from chess servers, condensed into a statistically representative .pgn file containing hundreds of different book lines.


Premier Division and the seasonal Superfinal are hand-selected openings, increasingly skewed at book-exit.  Nelson selects Premier openings and veteran bookmaker Jeroen Noomen (‘Jeroen_TCEC’) selects Superfinal openings.  Each of them take different approaches to openings selection that suit the competitions they serve.  Premier openings are eight moves.  Superfinal openings can be of any length.


Nelson tries to balance three objectives in his Premier picks: 1) to deliver the widest variety of opening systems, 2) to keep the overall draw-rate under 80% in any given season, and 3) to limit the instances of same-color wins from game-pairs to the greatest extent possible.  To find these positions Nelson uses his Catobase to look for positions that meet various criteria within his empirical and evaluative data.  He avoids book-exit positions where the next move is obvious, where pieces already have been (or are about to be) exchanged, or which have happened very rarely in his database.


Jeroen’s approach is less statistical and more chess knowledge-driven.  His process is to use leading chess engines to check if a line is obviously drawish or is certain to lead to heavy exchanges.  He judges whether a given position offers the prospect of a good fight with multiple playing options for both colors.  His opening picks always include a wide variety of systems, pawn structures and themes.  There are positional and sharp openings, those with short and long castling, gambits, main lines, antique and topical lines, and occasionally a dubious line.  (As long as dubious lines are not one sided they are fine.)


Please note that both Nelson and Jeroen admit that no engine—whether traditional or neural net—would pick their chosen opening lines themselves!  Their respective approaches are unbiased for precisely this reason.  They make their opening selections several months in advance, at which point they do not know which engines will be playing or where they will be seeded.  As noted earlier, TCEC needs playing variety as otherwise the engines would probably repeat a limited repertoire of openings and seldom, if ever, enter the kinds of critical lines that Jeroen in particular favors.


Q:  What do you mean when you say you “skew” openings, and why do you do it?

A:  Skew is synonymous with bias, i.e. the degree to which a particular opening, or a set of openings, seem to favor one side or the other according to empirical data (historical outcomes) and evaluative data (deep analysis from top engines).


The opening position typically offers white a slightly favorable evaluation of +0.15 to +0.20 on traditional chess programs.  Low bias is fine when the opponents are mismatched or are materially weaker than the best programs.  However, if played by the top programs on powerful hardware at long time controls such a small degree of bias invites a draw-rate approaching 90%.


To combat this tendency we introduce bias in the Premier division and to an even greater degree in Superfinals.


Q:  To what degree do you skew openings?

A:  In Premier Division Nelson is in his comfort zone when opening evaluations in traditional chess engines (i.e. not neural nets) are between +/-0.40 and +/-0.65, have a historical success rate of 62% or less and a draw-rate in the lower half of the median.  Sometimes he will deviate from these guidelines to the upside or downside for the purpose of satisfying opening variety goals.


In each season’s Superfinal Jeroen has a free hand to do whatever he thinks will result in an interesting and varied contest.  Sometimes his book-exit evaluations will exceed +/-1.00; sometimes he will offer speculative gambits.  His goal is to keep the draw-rate in the 65-80% range each season without any one-sided openings.


Q:  Why such an aversion to draws?  If chess is naturally drawish, why try to distort that reality?

A:  The ultimate objective of a tournament is to crown a deserving champion.  If you play 100 Superfinal games and 95 of them are draws you will not only drive away much of your audience but wind up crowning a champion that may have only scored three wins against his opponent’s two.  In such a case statistics tell us that the winner qualified for the Superfinal based on skill but may have won it on account of luck.


While we do not object to close contests in the Superfinal—on the contrary!—we would prefer as many decisive (i.e. not tied) game-pairs as possible, as this way the truly strongest competitor will have the greatest chance to demonstrate all-around superiority and entertainment value will be maximized.


Q:  How long can you maintain your targeted 65-80% draw-rate in the Superfinal when engines are continually improving?

A:  Draw abatement will definitely be more challenging as the competitors increase in strength in the years ahead.  A mental comparison between today’s leading chess programs and those of ten years ago, combined with a little extrapolation into the future, points to a time where something will have to give.  On the other hand, as long as neural nets and the best alpha-beta engines are competitive with each other their contrasting play-styles will help keep draw-rates lower than they otherwise would be.


Q:  What impact will the advent of neural nets and their very different evaluative frame of reference have on your opening set selections?

A:  Good question, and one we do not yet have an answer for yet.  For the time being, until there is more information, there will be little or no impact.  TCEC’s history is one of gradual evolution in response to emerging trends and practical experience; we expect that to continue.


Q:  How long have you been doing this and what are your respective qualifications for the job?

A:  Nelson took the openings reins in 2013, mid-way through Season 5, during founder Martin Thoresen’s period of directorship.  Jeroen took responsibility for the Superfinal at Nelson’s invitation before Season 9.


Jeroen has been active in computer chess since the early 1980s.  He has been associated with the Rebel and Rybka programs in the past as an opening book consultant and over the years has participated in numerous live computer chess tournaments in the Netherlands and elsewhere.


Nelson’s primary tangible qualification is his proprietary Catobase, now over 14 years in active development.  He was a participant in Anson Williams’ three-time champion freestyle chess team.  He has been enthralled by chess programs since 1982, when he bought Sargon II for his Apple II+.