Your games should become a library, not disappear after one report.

Zen is designed as more than a one-time engine report. It turns your Chess.com, Lichess, and PGN history into a personal learning workspace: keep every game, find its turning points with Stockfish, ask Cassia for the reasoning, branch with Explore, and continue unfinished positions with Simulation.

The problem

A bad-move label is the beginning of a useful review.

Chess engines are excellent at finding stronger moves, but an evaluation change does not automatically tell a player what they misunderstood. Cassia turns engine-grounded facts into a plain-language explanation of the threat, tactical detail, positional concession, or plan behind the move.

The workflow

Keep the game, find the moment, understand it, and try again.

Personal game library

Import games from Chess.com, Lichess, or PGN and keep reviewed games together in Dashboard.

Stockfish analysis

Analyze positions in the browser, classify moves, and move directly to the important turning points.

Cassia explanations

Ask why a move failed and connect the engine line to a concrete chess reason.

Explore and Simulation

Play another move yourself. If a player resigned or a better move went unplayed, let Simulation continue that exact position at a chosen strength.

Where Zen began

A tournament game ended. The chess question did not.

At a local tournament, Zen’s developer had an opponent resign from a position he thought they might be winning. He kept returning to a tactic they could have tried and wondering how he could counter it. Zen began as a way to keep that position, explore the unplayed move, and continue the game without losing its context. AI came later, when Cassia was added to help explain the engine-grounded reasoning.

Local by default

Start without an account. Analyze with the engine in your browser.

The core game library can be used locally, and Stockfish runs as WebAssembly in the browser. Account and optional AI-assisted features have separate data behavior described in the Privacy Policy and AI Disclosure.

Project notebook

Why a chess coach shouldn’t be allowed to invent the position

Cassia is built around a simple constraint: explanation should follow chess analysis, not replace it. The development note on Lichess explains the method, its limits, and why the work grew into Zen.