How Stockfish Game Review Works

Every game you review on ChessDeeper is analyzed move-by-move by Stockfish, one of the strongest chess engines in the world. For each position in the game, the engine searches ahead many moves deep to work out the best available move and how much the evaluation shifts after the move that was actually played.

That evaluation shift is what turns into the labels you see next to each move - Best, Excellent, Inaccuracy, Mistake, or Blunder. A small drop in evaluation might be an inaccuracy; a large one that hands the advantage to your opponent is a blunder.

ChessDeeper runs Stockfish directly in your browser using WebAssembly, so no server-side computation or waiting in a queue is needed - analysis happens locally on your device as you step through the game.

When your browser supports it, ChessDeeper uses a multi-threaded build of Stockfish that splits the search across several CPU cores for faster, deeper analysis. If that isn't available, it automatically falls back to a single-threaded version so the review still works, just a bit slower.