Modern Chess Openings, Fundamental Chess Openings, Wikipedia pages on openings,
Can anyone recommend a small opening book?



Fundamental Chess Openings isn't a small book, by any means, but quite often van der Sterren only goes 8 or 10 moves deep in a variation. He seems to prefer explaining why each move is made rather than simply list them. Sounds ideal for your application.

I think people are getting confused. Are you meaning an opening book for a chess engine, or a book on openings you can read? I'm thinking the former, but everyone else is thinking the latter.

"... Ideas Behind the Chess Openings ... cannot be recommended to the modern student seeking to improve his or her understanding of opening theory."
https://web.archive.org/web/20140708112658/http://www.chesscafe.com/text/review315.pdf

Modern Chess Openings for sure! I bought a copy of the 19th a couple years ago, I'm not sure if they have new editions since then, but they are always renewing it for additions to theory.

Modern Chess Openings ... I bought a copy of the 19th a couple years ago, I'm not sure if they have new editions since then, but they are always renewing it for additions to theory.
I have not seen a revision since Modern Chess Openings (15th ed.), published in 2008.
https://web.archive.org/web/20140626165820/http://www.chesscafe.com/text/hansen110.pdf
It's for my own engine matches? I'm not keen on the books available that are so large often when you use them the first like 20 moves can be taken from the book, I want as much of the game as possible to be moves from the engines. However if a book isn't used the engines will take ages on the very first moves. Is there any book that has only like 5 or 10 moves max?