Free Chess Analysis with Stockfish 18

ChessOnyx provides powerful, free chess game analysis directly in your browser using Stockfish 18 — one of the strongest chess engines ever created. No installation required. No account needed. Just paste your PGN and start analyzing instantly.

How to Analyze Your Chess Games

Analyzing your games with ChessOnyx takes less than a minute to get started:

• Import PGN: Copy your game PGN from Chess.com or Lichess and paste it into the import dialog. ChessOnyx supports standard PGN format including headers, comments, and variations.
• Fetch Games Directly: Connect your Chess.com or Lichess account to fetch your recent games automatically without copying anything.
• Configure the Engine: Choose your Stockfish version and adjust threads and hash memory to match your hardware for the best analysis speed.
• Start Analysis: Run a full move-by-move evaluation with accuracy scores, centipawn loss tracking, and best-line suggestions for every position.

What the Analysis Shows You

ChessOnyx analysis gives you a complete picture of your game, not just a list of mistakes:

• Move-by-move evaluation: Every move is scored against Stockfish's top choice using centipawn loss, so you know exactly how much each decision cost you.
• Accuracy score: A single accuracy percentage for each player, calculated using a strict centipawn-loss model that distinguishes between opening inaccuracies and critical endgame blunders.
• Best lines: See the engine's top suggestions for each position, with up to 5 principal variations so you understand the alternatives, not just the single best move.
• Opening identification: Every position is matched against a comprehensive opening database so you can see what opening you played and where you deviated from theory.
• Evaluation graph: A full game evaluation curve showing how the advantage shifted from move to move, making it easy to spot the critical moments.
• Phase-aware accuracy: The system treats opening inaccuracies differently from middlegame blunders and endgame mistakes, giving a more meaningful picture of your play.

Why Stockfish 18?

Stockfish 18 is the latest version of the world's strongest open-source chess engine. It uses a neural network evaluation function (NNUE) trained on hundreds of millions of positions, giving it superhuman positional understanding alongside its legendary tactical calculation. Running Stockfish 18 in your browser via WebAssembly means you get world-class analysis power on your own hardware — your games never leave your device.

Free and Privacy-First

The full analysis engine runs locally in your browser. Your games are never sent to any server for processing. Free accounts can save up to 10 games to cloud history. ChessOnyx Pro members get unlimited cloud storage and extended game history.

Tips for Better Analysis

To get the most out of engine analysis, consider these approaches:

• Analyze your own thinking first before consulting the engine — identify where you felt uncertain during the game.
• Use multiple principal variations (Multi-PV) to see whether your move was nearly as good as the engine's top choice, not just whether it matched exactly.
• Focus on positions where the evaluation shifts significantly, not every single move — these are the moments that decided the game.
• Let the engine run to sufficient depth (20+) before drawing conclusions. Shallow analysis can be misleading in complex positions.