How Do Chess Engines Work? | Secrets of AI Revealed

chess engines

Ever wondered how chess engines like Stockfish are able to beat even the best chess players in the world? You’re not alone. Chess engines seem almost superhuman in their ability to calculate millions of moves ahead and choose the best possible path to victory. But under the hood, chess engines are powered by algorithms and computing power, not actual intelligence. They rely on a technique called tree search to explore the game tree of possible moves and countermoves, evaluating the board at each step to determine the path most likely to lead to a win.

By calculating thousands of positions each second, the top chess engines today have become nearly unbeatable. But they still lack the human qualities of intuition, creativity, and positional understanding that the best chess players possess. Read on to discover how chess engines like Stockfish work their magic.

An Introduction to Chess Engines

So, you want to know how chess engines work, huh? These sophisticated software programs that can beat even the best human chess players are fascinating. Let’s take a peek under the hood.

The Basics

Chess engines evaluate positions and moves to find the best way forward. They analyze millions of possibilities, using algorithms to determine the value of each position. The engine picks the move that leads to the position with the highest value.

To do this, the engine first generates a huge tree of possible moves and resulting positions. It then evaluates each position to determine the material value (based on pieces left) as well as strategic value (center control, mobility, safety, etc.). Using a mathematical formula, it assigns each position a score.

The engine then looks for the sequence of moves that leads to the positions with the highest total score. This entire process happens in a fraction of a second! The engine can see far more moves and positions than any human player.

Improvements Over Time

Chess engines have become far stronger over time. Developers have improved their algorithms, added more data to help engines evaluate positions, and increased their speed and computing power.

Modern top engines like Stockfish and AlphaZero have been trained on millions of master games and can calculate up to 60 million positions per second! They employ advanced machine learning techniques that allow them to actually learn from their experience playing, just like humans.

With chess engines, this powerful, even grandmasters don’t stand a chance. But their superhuman skills are a testament to the remarkable power of artificial intelligence and modern computing. Chess engines are a fascinating example of technology advancing to superhuman levels.

How Chess Engines Evaluate Positions

When chess engines evaluate positions on the board, they go through a complex process to determine the best move.

First, the engine analyzes all the possible moves for both sides. For each move, it plays through potential sequences of future moves to see how the position may develop. It evaluates positions based on factors like material (which side has more valuable pieces left), space (which side controls more of the board), mobility (how much freedom each side’s pieces have to maneuver), and safety (how vulnerable each side’s pieces are to attack).

The engine then assigns a numerical value to each position to represent how good or bad it is for either side. Positions where White has a clear advantage may be +1 or higher, positions that slightly favor Black may be -1 or lower, and evenly balanced positions are 0.

Using a method called alpha-beta pruning, the engine can ignore sequences of moves that ultimately lead to positions it has already determined are worse than a position it has already found. This makes the search process much more efficient.

After searching all the way to the end of potential sequences, the engine backs up and chooses the move that leads to the position with the highest evaluation. This move is what the engine recommends as the “best” move for the current player.

Of course, chess engines aren’t perfect. They can’t possibly see every single sequence of moves and position, and their evaluations are limited by how accurately their algorithms can assess complex positions. But the best engines today have been programmed with sophisticated algorithms and have access to massive databases of master games, allowing them to play at a superhuman level.

Chess Engine Search Techniques

Chess engines use sophisticated search techniques to analyze positions and choose the best moves. As an engine calculates millions of possible moves, it employs pruning methods to narrow the search space.

Search Depth

Chess engines explore potential moves by “looking” several moves ahead, known as the search depth. The deeper an engine searches, the more accurate its analysis becomes. However, searching too deeply can slow down the engine and cause it to run out of time in a game. Engines must strike a balance between search depth and speed.


To avoid wasting time analyzing poor moves or redundant positions, engines use pruning techniques like:

  • Alpha-beta pruning: Ignores moves that won’t improve the position.
  • Quiescence search: Limits search depth in “quiet” positions with few captures or checks.
  • Transposition tables: Stores positions to avoid re-analyzing them.
  • Null-move heuristic: Skips analyzing responses to an opponent’s “null move”.

Evaluation Functions

An engine evaluates positions using an evaluation function that assesses factors like:

  • Material: Compares the value of the pieces each side has.
  • Mobility: Measures how freely each side’s pieces can move.
  • King safety: Assess each king’s exposure and vulnerability.

The engine chooses the move that leads to the position with the highest evaluation according to these criteria. By tweaking the weights of evaluation functions, programmers can refine an engine’s “style” of play.

Move Ordering

Engines don’t analyze moves in a fixed order. They use heuristics to analyze the most promising moves first. Moves are ordered based on things like:

  • Capture moves
  • Checks
  • Moves suggested by an opening book
  • Moves that have led to good positions in the past

By ordering moves intelligently, engines can find strong moves faster and search deeper. Move ordering, combined with pruning techniques, allows chess engines to play at a superhuman level.

Popular Chess Engines Throughout History

Chess engines have come a long way since the first ones emerged in the 1950s. As computing power has increased, chess engines have become far superior to humans. Let’s look at some of the most well-known chess engines throughout history.

Claude Shannon’s Chess Playing Machine (1950)

One of the earliest chess engines was created by mathematician Claude Shannon. His “chess playing machine” demonstrated the possibility of automating chess.

Mac Hack (1967)

Created at MIT, Mac Hack was one of the first chess engines that could actually play a full game. However, its algorithm was very basic and easy for skilled players to beat. Mac Hack showed the potential of computer chess but also how much progress was still needed.

Deep Blue (1997)

IBM’s Deep Blue made history as the first computer system to beat a chess world champion. In a famous match, Deep Blue defeated Garry Kasparov in a six-game match. Deep Blue could evaluate 200 million chess positions per second, proving that computers had become powerful enough to outplay humans at chess.

Stockfish (2008-present)

One of the top chess engines today is Stockfish, an open-source engine that can beat grandmasters. Stockfish can see an astounding 70 million chess positions per second. Regular updates have made Stockfish stronger and stronger over the years. As of 2023, Stockfish is ranked as the top engine in the world with an elo rating of >3500.

Chess engines have steadily advanced thanks to increases in computing power and improvements in algorithms. While humans once reigned supreme in chess, today’s chess engines far surpass even the best grandmasters. The future will likely hold even stronger chess computers that push the game to new heights.

The Impact of Chess Engines on Human Play

Chess engines have significantly impacted how humans play the game. While originally intended as a learning tool, chess engines are now far superior to humans and have shaped strategies and styles of play.

The engines are always improving.

As chess engines continue advancing, they are constantly reaching new heights in skill and computational power. Modern top engines like Stockfish and Leela Chess Zero have elo ratings over 3500, far surpassing even the best grandmasters. Each new version of an engine represents years of progress in neural networks, search algorithms, and processing power.

Engines never forget. Unlike humans, chess engines have instant recall of millions of positions, openings, endgames, and games. They never forget a tactic or strategic idea. This “perfect memory” allows engines to play theoretically perfect chess with the information available. Humans can never match this depth of knowledge and recall.

New strategies emerge.

Powerful engines have enabled new chess strategies and styles of play to develop. Positions once thought dubious are now mainstream, and new openings are frequently discovered. Engines can analyze countless positions to find small advantages and new ideas. These strategies are often surprising and counterintuitive, showing the depth of insight engines provide.

The impact of chess engines is felt at every level of chess. While they have pushed human understanding of the game to new heights, they have also highlighted our human limitations. Still, chess remains an art form, one where intuition, creativity, and imperfection continue to shape the beauty of the game. Though chess engines are a tool for progress, human insight and ingenuity will always be at the heart of the game.


So there you have it, a high-level view into the fascinating world of chess engines. These powerful algorithms have revolutionized the game of chess and continue to push the boundaries of artificial intelligence. While we may never fully replicate human intuition and creativity, chess engines demonstrate what is possible when we combine large datasets, pattern recognition, and brute force computational power. Next time you watch Magnus Carlsen take on Stockfish, you’ll have a deeper appreciation for the engineering marvels behind the scenes. Who knows, maybe someday an engine will solve chess once and for all. Until then, keep practicing your endgames!

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