I have seen some commentary that implies that Stockfish did not have access to an opening book in its much-reported match with AlphaZero, but I cannot find a conclusive citation, and my inability to do so has me wondering if maybe Stockfish did have an opening book after all.

For example:

GM Hikaru Nakamura...called the match "dishonest" and pointed out that Stockfish's methodology requires it to have an openings book for optimal performance. While he doesn't think the ultimate winner would have changed, Nakamura thought the size of the winning score would be mitigated.

or, from a StackExchange answer:

Stockfish...wasn't allowed to use an opening book which makes it consider many moves in shallow depths.

It's worth noting that even if Stockfish didn't have an opening book for the canonical 100 game match, page 6 of the paper shows that AlphaZero is dominant when you start from a variety of common openings. Nonetheless I wonder why they would handicap Stockfish this way.

  • 1
    Just FYI in April 2019 an updated version of AlphaZero was run against "a variant of Stockfish that uses a strong opening book". The results were more favourable to stockfish, but AlphaZero was still the overall winner by a convincing margin.
    – fostandy
    Commented Feb 16, 2020 at 13:06

3 Answers 3


Both Nakamura and the StackExchange answer were correct - Stockfish didn't use an opening book. I think Google did that to make a fair comparison as AlphaZero wasn't using an opening book as well.


I didn't see anything about opening book for Stockfish in the paper. I'm not the only one.


As far as I read the paper, I didn't see a book for Stockfish mentioned, so I guess, match was bookless.



While this is indeed incredible, show me how it beats SF dev with good book and syzygy on equal hardware in a 1000 game match.

  • Thanks @SmallChess. Is there a canonical source for this info? I did not find it in the paper.
    – kuzzooroo
    Commented Dec 12, 2017 at 2:29
  • @kuzzooroo I've added some links. There is no mention at all about opening book for SF in the paper. Please consider to accept my answer.
    – SmallChess
    Commented Dec 12, 2017 at 4:11
  • 7
    AlphaZero itself is a book, I don't think that the match is fair.
    – ferit
    Commented Dec 12, 2017 at 6:03
  • 1
    Opening books and tablebases are crutches that a whole generation of chess engine software has grown to become dependent on. The match is fair in the sense that both engines are not relying on pre-recorded moves to play at a higher level, the emphasis is on machine intelligence and not dictation.
    – prusswan
    Commented Dec 22, 2017 at 9:26
  • 1
    I still haven't found a canonical source for this, but there's discussion all over the place based on Stockfish not having an opening book.
    – kuzzooroo
    Commented Jan 28, 2018 at 19:06

To add to SmallChess's answer, Stockfish as an engine doesn't come with an opening book. Those are separate inputs, and you can give Stockfish whatever opening book you want. Therefore, if the AlphaZero paper doesn't say the authors gave Stockfish an opening book, it didn't have one.

See this thread on Chess.com for more about Stockfish playing with the Cerebellum opening book (aka "Brainfish"). You can see from the rating list that the opening book is worth about 50 elo - a substantial amount. You can also see the difference in the TCEC S14 superfinal, which was played with set openings, and the rapid bonus afterwards, played without books. Leela (an AlphaZero clone) narrowly lost the superfinal, but annihilated Stockfish in the bookless bonus.

  • Leela isn't quiet an AlphaZero clone, IMO.
    – Brandon_J
    Commented Mar 21, 2019 at 20:13

Stockfish stopped using opening books a long time ago. That is, it's an engine, and if you want to use an opening book, you have to use it in UI that you use to play the game or in the software you use to interface with the engine, playing book moves without even telling Stockfish about that.

There's no way to tell Stockfish about existing books (the commands were removed completely), and it's not expecting to use any.

OTOH, Stockfish can and would gladly use end game tables (Syzygy).

  • Given this fact it was harsh of Nakamura to call the match "dishonest" because of the lack of an opening book for Stockfish.
    – kuzzooroo
    Commented Dec 28, 2020 at 18:17
  • @kuzzooroo Nakamura is not a programmer, all minor implementation details of the engine interaction with GUI might have escaped him. Another tidbit would be, the games were not played from the initial position, but from some kind of preset position, in which case the importance of the opening book is not that crucial.
    – lenik
    Commented Dec 29, 2020 at 3:13

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