ChessOnyx — Free Chess Analysis with Stockfish 18

Powered by Stockfish 18 | 3M+ Puzzles & Free Analysis

How it Works

This platform allows you to evaluate your chess games and positions directly in your browser using the Stockfish Web Engine. With integrated analysis features, you can adjust engine parameters to find the right balance between speed and depth for your needs.

Please note that evaluation results, accuracy, and performance metrics should be seen as directional trends rather than absolute facts. All evaluations can fluctuate based on your hardware performance and calculation depth.

Quick Guide

To help you get started, here is a simple walkthrough on how to run your first analysis:

  • Copy Game PGN: After finishing a match on major platforms like Chess.com or Lichess, you can usually export or share the game as a PGN string.
  • Import PGN: Click the "Import" button and simply paste your PGN (Ctrl+V). The board will immediately update.
  • Select an Engine: Choose your preferred Stockfish version. You can fine-tune parameters like threads or hash memory by clicking the gear icon in the engine panel.
  • Start Analysis: Once ready, hit the "Start Analysis" button to begin the move-by-move evaluation.

For Members

If you want to skip the manual copy-pasting, you can take a shortcut: Use the "Fetch Games" button to directly link your Lichess or Chess.com accounts. Free members can save up to 10 games, while Pro members enjoy unlimited storage and full history integration.

The Evaluation Philosophy

The system is intentionally strict. The moves are compared directly with the engine's top choice, often resulting in lower accuracy scores than platforms that use more lenient models. This is a deliberate design choice — it rewards precise play and provides a more honest picture of your performance.

Rather than relying on linear material shifts, this system measures move quality by how it alters the mathematical win probability of the position. A move that throws away a decisive advantage is penalised much more heavily than an inaccuracy in a balanced position — because it should be.

From Evaluation to Win Probability

Engine evaluations (measured in centipawns) are converted into a win probability using a sigmoid function. This allows the system to distinguish between moves that are technically suboptimal but practically fine, and moves that genuinely damage your winning chances.

Contextual Severity: Opening vs. Endgame

The model factors in the game phase and remaining complexity on the board. An identical material loss in the opening is penalised less than the same loss in a simplified endgame where precision is everything. This makes accuracy scores meaningful across different game types and time controls.

Why did I build this?

I am a student with zero background in programming or web development. In my free time, I love playing chess. I always enjoyed tracking my progress through numbers and statistics, but I felt that high-quality analysis features should not always come with a steep subscription price.

With absolutely no initial knowledge of how to build a website, I decided to create my own platform. I wanted a place that provides the features I love as a player — tools that offer motivation and help me see exactly where I can improve my game.

Transparency & Support

I know it might look like just another site trying to hide features behind a paywall. But I give my best to keep the heart of this project — the Analysis — free for everyone. I only charge for features that cost me real money to maintain, like cloud storage for your history or server maintenance.

This is a one-man operation. Maintaining and expanding this site as a hobby takes a lot of time and resources. It is more than enough for me if you simply try out the site. Constructive feedback helps me immensely.

Chess Openings Explorer — 12 Openings with Variations

ChessOnyx includes a detailed chess openings explorer covering 12 of the most important openings, each with move-by-move explanations, key ideas, and multiple variations. Every opening page includes a full written guide with strategic commentary.

  • Queen's Gambit — One of the oldest and most respected openings. Covers the Accepted, Declined, and Slav variations.
  • Sicilian Defense — The most popular response to 1.e4 at all levels. Covers the Najdorf, Dragon, and Scheveningen variations.
  • Ruy Lopez — A classical opening with centuries of theory. Covers the Berlin, Marshall, and Chigorin variations.
  • French Defense — A solid, strategic choice for Black. Covers the Winawer, Tarrasch, and Exchange variations.
  • Italian Game — A rich positional opening with sharp attacking potential. Covers the Giuoco Piano, Evans Gambit, and Two Knights variations.
  • King's Indian Defense — A dynamic hypermodern defense. Covers the Classical, Sämisch, and Four Pawns Attack variations.
  • Caro-Kann Defense — A solid and reliable defense against 1.e4. Covers the Classical, Advance, and Exchange variations.
  • London System — A flexible, low-theory system for White. Covers the main setup, King's Indian setup, and reversed London variations.
  • Scandinavian Defense — An aggressive and direct response to 1.e4. Covers the Main Line, Mieses-Kotrč, and Icelandic Gambit variations.
  • King's Gambit — A romantic, attacking gambit with rich tactical play. Covers the King's Gambit Accepted, Falkbeer Counter-Gambit, and Modern Defense variations.
  • Fried Liver Attack — One of the sharpest and most aggressive lines in chess. Covers the main Fried Liver, Traxler Counter-Attack, and Lolli Attack variations.
  • Traxler Counter-Attack — A daring gambit response to the Fried Liver. Covers the main line, Bishop sacrifice, and Knight sacrifice variations.

Chess Articles — 8 In-Depth Guides

ChessOnyx publishes in-depth articles on chess improvement, engine analysis, and the science behind chess tools. Each article is written for players who want to understand not just what to do, but why — covering practical topics backed by engine data and chess theory.