How Does Stockfish Work? The Engine’s Blueprint Simply Explained

Stockfish applies highly complex formulas and calculations to analyze each move throughout a chess game.

To do this, Stockfish performs three ongoing processes that influence each other: position evaluation, finding candidates, and computing the optimal moves.

Although other engines use similar processes, Stockfish is currently the world’s most powerful chess engine.

Why is that? In this post, we’ll provide a complete answer to: How does Stockfish work? What makes it such a powerful engine?

How Does Stockfish Work? The 3 Main Processes of the Engine

Here are the three stages Stockfish goes through to provide accurate analyses:

1. Evaluate Positions

The engine continuously evaluates the positions of the game from the opening to the endgame.

To do this, Stockfish uses various evaluation criteria, including material balance, king safety, pawn structure, etc.

Here are some scenarios that the engine considers to get a context of what is happening on the board:

  • Material advantage gives the player an upper hand over their opponent.
  • Controlling the center area of the board is a good thing.
  • Defending and protecting the important pieces give you more weight.
  • Attacking the opponent’s powerful pieces increases your dominance.
  • Having pawns controlling the center of the board is advantageous.
  • Having pawns isolated is a bad thing.
  • If one or both bishops control the diagonal line on the board, you’re in a good situation.
  • Encircling the king with your other pieces is favorable.
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2. Find Candidate Moves

After evaluating the current game position, Stockfish searches for the possible moves that can result from that situation.

However, the engine doesn’t calculate all the possible moves from that point until the draw or checkmate.

That’s because there’s an infinite number of possible moves in a chess game.

Instead, the engine only looks ahead as far as possible based on its maximum depth.

The engine constructs a search tree to find candidate moves, including the possible plays and what moves these can result in.

It continuously increases the tree branches until it reaches the assigned maximum depth or time.

3. Compute the Optimal Moves

Stockfish employs heuristics based on the game’s current stage to assign different values to each candidate move.

The engine also uses an algorithm called alpha-beta pruning to eliminate possible ineffective moves from the tree. In addition, it takes the frequently encountered positions into account.

Stockfish performs hundreds of thousands of calculations in a few seconds. Ultimately, it identifies the best 1–5 moves you can make based on your current position.

How Many Moves Does Stockfish Calculate?

Stockfish calculates as many moves as possible, depending on the game’s current position, the maximum depth, and the used processor’s power.

The engine can predict an immense number of moves ahead. Still, there are no available statistics on the exact number of plays it can anticipate.

The engine keeps calculating optimal moves and eliminating inefficient ones as long as it has time.

How Does Stockfish Search So Deep?

Stockfish searches deeply by constructing a tree of vast possibilities and evaluating each of them.

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The engine eliminates the moves that have a bad score or, in other words, are inefficient.

After that, it constructs new layers or branches of the tree based on the good possibilities. The process continues until the engine reaches its maximum depth.

Does Stockfish Use Machine Learning?

Yes, Stockfish uses neural net architecture in its latest versions, which is a type of machine learning.

It uses this technology in addition to alpha-beta pruning and Minimax algorithms to analyze positions and calculate optimal moves.

The engine has been using machine learning in its core system since the launch of Stockfish NNUE in 2018.

Adding the neural network to Stockfish has allowed its developers to expand the training data of the engine significantly.

As a result, Stockfish’s Elo rating has increased considerably over the past few years to reach 3534 as of 2022.

This substantial rise in its Elo rating has pushed the Stockfish ranking to become the world’s best chess engine from 2018 until today.

Can a Human Ever Beat Stockfish?

No human chess player of any level has beaten the latest version of Stockfish so far. With its immense power, it’s nearly impossible for a human to defeat this engine.

Stockfish has been trained for over a decade to become today’s most potent chess engine.

However, a few people managed to beat Stockfish in his early versions, like Stockfish 8.

Still, there’s a significant difference in power between these early versions and today’s engine, Stockfish 15.

Is Stockfish vs. Stockfish Always a Draw?

When Stockfish plays against itself, it’s highly probable the result will be a draw. Still, this isn’t always the case.

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Although Stockfish is designed to reach optimal moves, it’s not perfect. The engine can make inaccurate moves from one time to another.

That way, when stockfish plays against itself, it’s possible for one of the versions to defeat the other.

This is especially likely when the time allotted for each move is limited. That’s because time limitations can lead to variations in the search depth of the engine.

Does Stockfish Ever Make Mistakes?

If you use Stockfish at low depths, it may make inaccurate assumptions. However, when used in its full depth, it’s difficult, if not impossible, for Stockfish to make a mistake.

The strongest chess engines, including Stockfish, have robust algorithms allowing them always to recommend and play the best moves.

Still, the quality of plays may vary slightly depending on the engine’s depth.

The Bottom Line

How does Stockfish work? The powerful chess engine performs three ongoing processes to provide the most accurate moves recommendations.

It evaluates the games’ positions, searches for possible plays, and computes optimal moves. It does this using a set of algorithms and neural net architecture.

Stockfish’s results vary depending on the assigned maximum depth and the device’s processing power. Nonetheless, it is still a reliable engine in all cases.

This impressive power of the current Stockfish version makes it nearly unbeatable by any human.