Question 1

Is it really free?

Accepted Answer

Yes. Reviewing games on your own device is unlimited and free, with no card and no sign-up. Analysis on our servers, where offered, has a fair-use daily limit so it stays free for everyone.

Question 2

Do I need an account?

Accepted Answer

No. Everything works without one. Games and analyses are kept in your browser, and you can export or delete them at any time from "Your data".

Question 3

Does my game leave my device?

Accepted Answer

Not unless you choose to. The engine runs inside your browser. Games are only sent to us if you sign in and ask for server analysis or cloud sync.

Question 4

Which engine does it use?

Accepted Answer

Stockfish 19, compiled to WebAssembly (Stockfish.js). Stockfish is free software under the GPLv3; the Licences page links to its source. The first visit downloads the engine, about 94 MB, and your browser keeps it afterwards.

Question 5

How are the move labels decided?

Accepted Answer

From the change in your chances of winning after each move, the same idea other review tools use. We check the labels against a set of annotated games.

Question 6

Is this connected to Chess.com or Lichess?

Accepted Answer

No. It is an independent project, not affiliated with, endorsed by or sponsored by Chess.com or Lichess. It only reads the public game lists those sites offer.