How Luftchess works
What happens between your game and the one idea you see.
From your game to one idea
Sign in with Lichess
You tap Sign in and Lichess asks whether Luftchess may know who you are. Luftchess reads your username, checks it against the list of invited players, and hands the access back to Lichess at once. It never asks for a password or an email address, and it cannot post, play or send messages for you.
The games come in
Luftchess asks Lichess for the recent public games of the username it is set up with. Today that is one player; accounts that each bring in their own games are being built. Only standard chess is read; variants such as Chess960 are skipped. Public Chess.com games can be read by username too. New games are looked at overnight, when the server is quiet.
The moment that mattered
Open Games and choose the newest game. Luftchess shows the moment it turned: one better move and one reason, with a board to try it on.
What “looked at overnight” means
Stockfish, the strongest open-source chess engine, goes through every move of the game on our server. It takes a careful look at each position, and a deeper second look at the moves it flags, before anything is shown to you.
Its scores are turned into a win chance: out of 100, how likely the side to move is to win from here. A move is judged by how much of that chance it gave away, not by raw engine numbers. We talk in pawns and plans, not centipawns.
When seven pieces or fewer are left, the Lichess tablebase gives the exact result of the position instead of an estimate: win, draw or loss with best play.
Nothing is explained unless the engine agrees with the explanation. When a clear reason cannot be checked, Luftchess shows the better move and says less.
What the verdict words mean
On the Analyse board, each move gets one word, judged by how much win chance it gave away compared with the engine’s best move.
| Word | What it means |
|---|---|
| Best | The engine’s first choice. “Only move” means every other move gives away a lot. |
| As good | Within 2 points of the best move’s win chance. |
| Good | Gives away less than 5 points. |
| ?! Inaccuracy | Gives away 5 to 10 points. |
| ? Mistake | Gives away 10 to 15 points. |
| ?? Blunder | Gives away 15 points or more. |
| Book move | A known opening move. |
What Luftchess does not do
- It does not help during a game. It only looks at games that have finished. Using an engine during a game breaks the fair-play rules of Lichess and Chess.com.
- It does not offer sign-in with Chess.com yet.
- It is not a course library, and it does not post anything anywhere.