About
A chess review that runs on your own machine
Checkmate Central hands your game to Stockfish and shows what each move actually cost. Nothing is uploaded.
- FreeEvery feature, no account.
- In your browserYour games are never uploaded.
- Stockfish 18The engine, on your own computer.
- Every levelMost useful if you are starting out.
What you can do here
- Review a gameFrom chess.com, Lichess or any PGN, every move graded with what it cost.
- Take the lessonsShort, one habit each, with positions checked by the engine.
- Play the botIt plays like a learner and warns you before a blunder.
- Learn an openingThe traps people fall into, and a board to practise each.
Where every number comes from, and what our own checks have caught: how we check what we publish.
Why it exists
Knowing a move was a blunder is the easy part, and every site gives you that much. What changes how someone plays is the rest of it: how much the move actually cost, which of your mistakes keep coming back, and what would have happened if you had played the move you first thought of. Those three are what this was built to answer. The exact thresholds are published in the guide to how moves are graded.
The second reason is simpler: a chess engine is a program that runs on a computer, and you already have one. There is no technical reason your games need to be sent anywhere to be analysed, so they are not.
How the analysis works
The engine is Stockfish 18, compiled to WebAssembly and run in a background thread inside your browser. When the page can be cross-origin isolated it uses the multi-threaded build on up to four cores, keeping one free so the board stays responsive.
Every game is looked at twice:
- A scan. Every position in the game is searched to a fixed shallow depth. This is what produces the first grade for each move and fills the move list as it goes.
- A second look. The moves that lost real ground are searched again, deeper — up to a dozen of them, worst first. A move is only ever compared against a search of the same depth, because comparing a deep evaluation with a shallow one invents mistakes that were never played.
Grades come from win probability rather than raw centipawns: dropping from +9 to +7 is not the same kind of error as dropping from +1 to −1, even though the pawn count moved further in the first case.
How the lessons are made
The lessons are written with newer players in mind, because the same few habits decide most of their games, but they are open to anyone. Their positions are not taken from grandmaster games: a deliberately weakened Stockfish plays itself, so the positions look like the ones a beginner reaches, and the real engine then verifies every answer. A free piece really is unprotected, a mate really is a mate, and a wrong move is only given a reason when the engine's own line shows it. Progress is kept in your browser and goes nowhere else.
What it will not do
It will not help you cheat. The tool is built for looking at games that are over; using an engine during a live game is cheating, and it will get you banned from every site worth playing on.
It also will not pretend to be certain. Grades are an engine's opinion at a fixed search depth, and a deeper search sometimes disagrees with a shallower one. Treat a borderline verdict as a prompt to look at the position yourself.
Built with
- Stockfish 18 (GPL v3) for the analysis, as a WebAssembly worker.
- chess.js for move legality and notation, react-chessboard for the board.
- Next.js and TypeScript, with IndexedDB for the evaluation cache so a position is never paid for twice.