What is the "cloud database"?
The cloud database (ChessDB) is a free-to-query online database at chessdb.cn.
It contains a huge number of positions, scored by back-end servers, and also some endgame tablebases. It can therefore be divided into an opening book and an endgame tablebase. If a move's note on the right contains any of the letters W/D/L, the current position is in the cloud database's endgame tablebase; otherwise it is not. See What is an "opening book"? and What is an "endgame tablebase"?
Apart from the endgame tablebase, the scores of positions in the cloud opening book are not necessarily accurate, but the more extensions a position has been calculated through, the more likely its score is accurate.
In addition, some commercial opening books are also accessed in the cloud-database way to prevent cracking.[1]
Commercial opening books only adopt this access method. They do not use the official cloud database address, but replace it with their own cloud database address. ↩︎