About ChessOnyx

The story behind the platform — who built it, why, and what it stands for.

Quick Guide

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

  1. 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.
  2. Import PGN: Click the "Import" button and simply paste your PGN (Ctrl+V). The board will immediately update.
  3. Select a Computer: Choose your preferred Stockfish version. You can fine-tune parameters like threads or hash memory by clicking the gear icon in the computer panel.
  4. Start Analysis: Once ready, hit the "Start Analysis" button to begin the move-by-move evaluation.

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.

How It Started

ChessOnyx started as a personal project. I'm a student who likes to play chess every once in a while in my free time — and it was pretty annoying that I couldn't analyze my games without paying for a subscription.

So I taught myself to build a website from scratch. ChessOnyx is the result — built by a casual chess fan, for like-minded players. Every feature exists because I wanted it myself.

The Philosophy

The core of ChessOnyx — the analysis engine — will always be free. Stockfish 18 runs directly in your browser, on your hardware, with no data sent to any server. Your games stay private. Your analysis is your own.

Membership exists only to support the running costs of the platform and to unlock features that require server infrastructure, like unlimited cloud game history. It is never a gate to the essential tools.

Technical Overview: The Accuracy Model

Rather than relying on linear material shifts, this system measures move quality by how it alters the mathematical win probability. By stepping away from standard Centipawn Loss (CPL), the model mirrors the practical swings of a real chess game.

1. From Evaluation to Win Probability (WP)

Computer evaluations (measured in centipawns) are converted into a win probability (WP) using a sigmoid function. This approach recognizes the diminishing returns of a material advantage: gaining +1.00 in an equal game can be game-changing, whereas gaining +1.00 when already leading by +8.00 is negligible.

The relationship is expressed as:

WP=11+e−k⋅cpWP = \frac{1}{1 + e^{-k \cdot cp}}

Where cp represents the computer evaluation and k is a scaling constant governing the curve's sensitivity.

2. Contextual Severity: Opening vs. Endgame

The model factors in the game phase and the remaining complexity on the board. This explains why an identical material loss can yield different accuracy scores depending on when it occurs:

  • High Complexity (Opening): The "drawing margin" is broad in the opening. A small loss, such as a pawn, often results in a relatively minor drop in WP because the position remains sufficiently complex to allow for positional or tactical compensation.
  • Low Complexity (Middlegame/Endgame): As pieces are traded and the board simplifies, the game becomes more "solved." A material loss here causes a sharp drop in WP, because there are fewer variables to obscure the disadvantage, making it more straightforward for an opponent to convert a lead into a forced win.

3. Accuracy Score Calculation

The final accuracy is determined by the Win Probability Loss (L), which is the difference between the computer's best possible move and the move actually played:

L=WPbest−WPplayedL = WP_{best} - WP_{played}

To map this loss into a human-readable percentage, an exponential function is applied. This ensures the system remains sensitive to small inaccuracies while harshly penalizing blunders that significantly alter the outcome.

Accuracy=100⋅e−α⋅LAccuracy = 100 \cdot e^{-\alpha \cdot L}

What ChessOnyx Offers

  • Free move-by-move game analysis powered by Stockfish 18
  • 3 million+ chess puzzles, filterable by theme and difficulty
  • Chess openings explorer with detailed explanations and variations
  • In-depth articles on engine analysis, hardware, and chess improvement
  • Direct game import from Chess.com and Lichess accounts

Transparency & Support

This is a one-man operation maintained as a hobby. I charge only for features that cost real money to run — cloud storage, server capacity, and infrastructure. Everything else is free, and I intend to keep it that way.

If you find ChessOnyx useful and want to support its development, a membership or donation makes a real difference. But simply using the platform and sharing it with other chess players is already more than enough.

Expertise & Credentials

ChessOnyx is built and maintained by a developer with hands-on experience in chess engine integration, WebAssembly deployment, and chess data analysis. The platform has served tens of thousands of chess players since launch, with analysis powered by Stockfish 18 — the world's strongest open-source chess engine. All articles and opening guides are written based on established chess theory and verified against engine analysis.

Special Thanks

JPTheKuma

A huge shout-out to JPTheKuma, a Twitch streamer who uses ChessOnyx live on stream. Seeing the platform used in real-time on stream means everything to me. If you enjoy chess content, check out his stream — twitch.tv/jpthekuma

Lichess.org

An extra special shout-out to Lichess. Their API powers game fetching, their opening explorer drives the theory database, and their commitment to open-source software has saved me from many sleepless nights. The PGN viewer, the board logic, the opening data — Lichess gives it all away freely so others can build on it.

Chess.com

Thank you to Chess.com for their public API that allows ChessOnyx to fetch games and player data directly. Without access to this data, a huge part of what this platform does simply wouldn't exist.

Stockfish

The beating heart of this entire platform. Stockfish is the world's strongest open-source chess engine, and it runs entirely in your browser via WebAssembly. None of the analysis, accuracy scores, or engine lines would exist without this incredible piece of open-source software.

Chessground

Every chess board you see on this site is powered by Chessground, the open-source board UI library built by the Lichess team. It handles piece rendering, move animations, arrows, and highlights — all the visual magic that makes the board feel alive.

chess.js

All the chess logic under the hood — move validation, PGN parsing, FEN generation, legal move calculation — is handled by chess.js. A reliable and battle-tested open-source library that quietly powers everything behind the scenes.

Get in Touch

Questions, feedback, bug reports, or just want to say hello — I read every message.

info@chessonyx.com