Stockfish Chess Engine

What is Stockfish Chess Engine?

Stockfish is a free, open-source chess engine originally derived from Glaurung, created by Tord Romstad. The name "Stockfish" is a Norwegian word for dried cod—a nod to the engine's Norwegian origins. Since 2008, hundreds of developers have contributed to making Stockfish the most powerful chess analysis tool in existence.

Unlike commercial engines, Stockfish is completely free under the GPL (GNU General Public License). Anyone can download, use, modify, and distribute it. This openness has fueled its rapid development and widespread adoption across chess platforms worldwide.

How Strong is Stockfish?

Stockfish's strength is almost incomprehensible. To put it in perspective:

A 600-point ELO difference means the higher-rated player is expected to win virtually every game. Even giving Stockfish material odds (removing pieces) doesn't help humans much—Stockfish plays so accurately that it converts small advantages with perfect precision.

How Stockfish Works: The Technology Behind the Engine

Stockfish combines two powerful technologies to achieve its incredible strength:

Alpha-Beta Search

At its core, Stockfish uses alpha-beta pruning—an optimized version of the minimax algorithm. It builds a tree of possible moves, looking 20+ moves ahead, and prunes branches that can't possibly be better than already-found alternatives. Modern Stockfish searches millions of positions per second.

NNUE Neural Network Evaluation

Since Stockfish 12 (2020), the engine has used NNUE (Efficiently Updatable Neural Network) for position evaluation. This neural network was trained on hundreds of millions of positions and provides nuanced positional understanding that traditional hand-crafted evaluation functions couldn't match.

The combination of deep search and neural evaluation creates the strongest chess engine ever built. Our chess calculator uses this same technology for instant position analysis.

Stockfish vs AlphaZero: The Famous Match

In December 2017, DeepMind's AlphaZero made headlines by defeating Stockfish 28-0 (with 72 draws) in a 100-game match. AlphaZero used pure neural network evaluation with Monte Carlo Tree Search—no traditional chess knowledge.

However, important context: AlphaZero faced Stockfish 8, an older version without NNUE. The match also used conditions that disadvantaged Stockfish (limited hash memory, no opening book).

Today's Stockfish 17 with NNUE incorporates neural network evaluation while keeping the powerful classical search. Most experts believe modern Stockfish would be extremely competitive with AlphaZero—possibly equal or stronger.

Stockfish Versions: Which Should You Use?

Our platform uses different Stockfish versions for different purposes:

• Stockfish 17: Latest and strongest. Used for analysis and bot battles (ELO 1320-3190). Features UCI_Elo for accurate strength simulation.
• Stockfish 11: Used for community puzzles. Allows "fantasy" positions with extra pieces that newer versions reject.

For most users, Stockfish 17 is the right choice. It's what powers our game analyzer and position calculator.

How to Use Stockfish Chess Engine Online

You don't need to download anything to use Stockfish. Our platform provides several ways to access its power:

Position Analysis

Our chess calculator uses Stockfish 17 with depth 18 analysis. Set up any position, click analyze, and instantly see the best move, evaluation score, and alternative lines. Upload screenshots from any chess platform—our image scanner detects positions automatically.

Game Analysis

Our AI game analyzer reviews every move in your game, classifying each as brilliant, good, inaccuracy, mistake, or blunder. You'll see exactly where you went wrong and what you should have played.

AI Opponents

Our 11 AI bots are powered by Stockfish with adjustable strength. Using the UCI_Elo parameter, we simulate opponents from 400 ELO (complete beginner) to 3600 ELO (full Stockfish strength). Practice against the perfect training partner at any level.

AI vs AI Mode

Watch Stockfish play against itself to see perfect chess. Our calculator features an "AI vs AI" mode where you can observe the engine's strategies and learn from its choices.

Understanding Stockfish Evaluation

When Stockfish analyzes a position, it gives an evaluation score. Here's what the numbers mean:

• +1.5: White is ahead by about 1.5 pawns worth of material/position
• -2.0: Black is ahead by about 2 pawns worth
• 0.0: Position is roughly equal
• +M3: White has forced checkmate in 3 moves
• -M5: Black has forced checkmate in 5 moves

Generally, an advantage of +1.0 is significant, +2.0 is usually winning with accurate play, and +3.0 or more is nearly always decisive.

Stockfish for Chess Improvement

Stockfish isn't just for analysis—it's a powerful training tool:

• Post-game analysis: Review every game to find mistakes and missed opportunities
• Opening preparation: Check your opening ideas against engine evaluation
• Endgame study: Learn precise technique in complex endgames
• Puzzle verification: Confirm tactical solutions are actually correct
• Sparring practice: Play against calibrated strength for realistic training

The key is using Stockfish to learn, not just to find answers. When the engine suggests a move you didn't see, ask yourself: "Why is this better? What did I miss?"

Is Using Stockfish Cheating?

This depends entirely on context:

• Cheating: Using Stockfish or any engine during rated games (online or over-the-board). This will get you banned from platforms and tournaments.
• Legitimate: Using Stockfish for post-game analysis, training, study, and improvement. This is encouraged and how most players learn.
• Legitimate: Using Stockfish for casual, unrated games where both players agree to allow it.

All major platforms (Chess.com, Lichess, FIDE) strictly prohibit engine use during rated play. Fair play policies detect engine-like moves and result in account bans. Use Stockfish ethically—for learning and improvement, never for cheating.