How can there be “weak” chess bots?

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In today’s day and age, computers are obviously way better at chess than humans, and even the best players in the world have a hard time holding a candle to engines like Stockfish, etc. However, what I don’t understand is how is it possible to have them in different levels of strength. For example, on Chess.com, there are dozens of bots that you can play against depending on your own level. But for the weakest ones, how does this work? One would think that an engine either knows how to play chess efficiently, or it doesn’t. How can you “dumb down” a computer to the level of an intermediate player or even a beginner? Thanks!

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Anonymous 0 Comments

The easiest ways to dumb down a chess engine are to limit the amount of time it has to select a move, limit the “depth” (number of moves in the future) it can analyze, or to have it pick randomly from a set of possible moves.

Chess computers, like humans, take time to find the right answer, and they can’t instantly see a mate in 10. Of course, give a computer a few minutes (or, usually, a few seconds), and they’ll see farther and more accurately than even the best humans. So limit those options, and it all of a sudden becomes much weaker.

But the engines that play against lower-level players, they’re set to more-or-less randomly pick between their possible candidate moves. A top-tier chess engine will almost instantly eliminate a move that loses its queen in 5 moves – unless it can gain something from that sacrifice. A medium-strength chess engine might eliminate the moves that lose a queen, but not the moves that lose a pawn or a bishop, and choose from there. And a chess engine for beginners might not eliminate any moves – it will leave pieces undefended so that beginning players can discover tactics and win games, while they work on their skills and level up to harder bots.

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