Top human players tend to not make the moves engines make. They also stay relatively strong when under time pressure, where lots of humans reentering moves from a computer fail.
Playing someone taking 10 seconds for each move— whether there is only one valid move to capture back or the situation is complicated— you get suspicious. And then when they forget how to play when they have 3 seconds per move stands out.
Chess.com has a measurement for how accurate a player plays compared to top engine moves called Computer Aggregated Precision Score (or "CAPS"), and top humans do play incredibly accurately. Magnus has CAPS of 98.36 for example.
I think that as a measure of skill vs. a computer that statistic doesn't tell you all that much. Note that even in that measure Magnus only picks the top move ~85% of the time, and that includes many moves where the top move is "obvious" which will inflate the average a bit. And it needs to be kept in mind that Magnus cannot win against a modern computer, so clearly that 85% only means so much, computer play is still on a whole different level from human play.
Beyond that, time is a very important factor, running out the clock is one of the most effective ways to win against cheating opponents. Magnus only finds the top move ~85% of the time and takes probably 10x to 100x the time to do it. And like the other commenter noted, variance in the move time is an extremely obvious tell. Magnus will blitz out certain moves (even in classical chess) and then think for ~40 minutes in other complicated positions. A computer can do both positions in basically the same amount of time, and cheating players typically don't know when they "should" be thinking vs. playing fast.
Note that even his "top engine match" is 85%. This is not a fantastically high number, given that maybe 40% of moves are obvious/must-moves. I bet I match the engine ~60%.
I also think this is his classical games, not rapid, blitz, or bullet.
Top human players tend to make safer, lower variance moves than things engines prove super safe on evaluation. They may give up a few centipawns for ease of analysis.
If nothing else, the time issue is a huge one. Cheaters have very consistent seconds-per-move while actual masters make obvious moves instantly and pause on tougher moves.
I suppose that only completely newbie cheaters would think of taking the same amount of time to make each move. It’s like the first rule of pretending to be a human: add a random delay to all of your actions.
And yet time and time again, chess streamers and content producers run across people with newly formed accounts and perfect win records playing the best engine move at regular measured intervals.
If you are cunning enough to hold off on the best move for a few extra seconds to appear unaided by an engine, or if you blunder X% moves in your game (or simply play the 3rd or 4th rated move which still probably wins against most humans), chances are you'd do fine learning some chess strategy and playing the game unaided.
People keep asking why one would cheat at chess. I'm sure there are some bad actors who aim to disrupt the game, in a manner consistent with cheater motivations in other games. I'd imagine many cheaters are simply looking for some quick dopamine after being frustrated by a plateau in their skill.
A random delay is also a tell, though. An obvious move shouldn't take 15 seconds, but if that's what the random delay for that move is, that looks suspicious. A more difficult move shouldn't take only 3 seconds, but if that's what the random delay for that move is, that also looks suspicious.
Definitely, random time is adding no correlation where it would count. Move time is an easily captured psychometric observation, the clever bit is that it’s intermingled with automated chess analysis.
Feels like there could be a lot of surprising inferences to think about here … just a few quick thoughts - how long does someone pause after a blunder, how does one react to unpredictable moves. Can definitely imagine AI being of significant utility here.
In general you’re right, but there are some tells because humans don’t have a random delay. It’s connected with the complexity (from the perspective of how humans think, which is different from engine calculation) of the position. One of the things that makes cheaters stand out is they will have a random weird delay on various obvious moves.
I thought it was a reasonably good answer considering that the question doesn't explicitly spell out why it might flag someone like Magnus Carlsen (who I learned is a grandmaster and World Chess Champion). To rephrase it, Irwin doesn't flag people for playing well — it alerts moderators when it finds suspicious signals across several dimensions.
