A Google researcher has figured out how to predict each card his opponent will play in mega-popular online card game Hearthstone. Don't (or do) worry, though: the tool he developed is staying locked away forever.

Google anti-fraud and abuse research lead Elie Bursztein developed machine learning/data analysis tech specifically for Hearthstone, which he demonstrated in this Defcon talk:


The short version? Bursztein's tool gets to the heart(h) of Hearthstone by "using data analysis to find undervalued cards and exploits game structure using machine learning to predict your opponent's deck." If you're interested in the math behind it all, he begins digging into this infernal contraption's nuts and bolts at around 14:30 of the video. Alternatively, this blog post really gets to the bottom of it.

Basically, though, the tool analyzes pre-existing decks and play strategies based on over 50,000 game replays and then collects and analyzes further data as matches go on. After a little while, it gets pretty absurd:


"The accuracy peaks between turn 3 and 5. Here the algorithm is able to predict what is the most probable card the opponent has in hand, but hasn't played, with an accuracy above 95%. The tool will get 80% of its predictions correct if you ask it for the 5 most likely cards the opponent has in its deck, and 56% correct if you ask for 10 cards."

Obviously, this sort of thing could break Hearthstone into a million-billion little pieces, but once upon a time Bursztein was planning to let anybody get their hands on it. Blizzard, however, wasn't so keen on the idea:

"One thing you won't see posted, however, is a software tool that we promised to release during our Defcon presentation. Following Defcon we had a series of conversations with the Hearthstone team about our research — apparently the email that I sent prior to Defcon didn't reach the right person. They like our research on game/cards balance and are very enthusiastic and supportive about it."

"On the other hand, they were very concerned that our real time dashboard that can predict your opponent's deck will break the game balance by giving that person (that is, whoever has the tool) an unfair advantage. They also expressed concern that such a tool makes the game less fun by taking away some of the decision-making from the player. It was a difficult decision — I invested a lot of our time building our real-time dashboard tool with Celine — but we agree with the Hearthstone team and will not release the tool publicly."

Meanwhile, Blizzard is planning to add replay functionality to Hearthstone itself, so that element of Bursztein's tool—while seemingly useful—is just a "subpar" version of a feature everyone will have access to soon.

This is all pretty wild, though. Even in the mythical (and cardboard) realm of Azeroth, machines rule. Or at the very least, they come up with some damn good tricks.