LaviChess is built so that chess feels alive. The pieces breathe, worry and celebrate, and you play against twenty-five opponents, each with a style of their own. Around the board is everything you need to get better: rules, openings, tactics, famous games, the daily puzzle and an analysis board. LaviChess is the English sister of Schackdags, a chess site in Swedish: the same game, the same characters, the same house.
Why Lavi?
Lavi (say LAH-vee) is a lion, and his name means just that, lion, in Hebrew. He is the strongest player in the house, and the site carries his name.
Who makes LaviChess?
LaviChess is made by Tentmaker Sweden, a sole proprietorship in Sweden (company registration number 701101-5034), which also makes Schackdags. Found a mistake in a rule, a game or a translation? Write to hello@lavichess.com and we will fix it.
Fair and safe
LaviChess has no chat, no account and no ads on the board. Children play here. How we handle data.
How LaviChess works
The technical part, for the curious.
The computer that plays
All the chess the computer plays on LaviChess is played by Lavi, our own chess engine, which we built from scratch. The strongest player in the house has the same name, because he is the engine itself: when you face Lavi, the engine plays at full strength. The other opponents use the same engine but get to think less, and they have their own taste and their own mistakes. Lavi also does the thinking for the analysis board, the review of your games, the Coach and the practice against the computer. It runs in your own browser, so your moves are never sent to us. Doris the Cat and Gus the Gull manage without it: Doris moves at random, and Gus takes whatever he sees.
When the computer reviews a move, it compares it with the best move in the same position and turns the difference into a chance of winning. A move is marked as a mistake only when the difference is so large that the mark is right at least nine times in ten. We tested that against a much stronger engine on 300 games that real players played on Lichess, from beginners to club players.
The opponents differ in strength because the computer may calculate a different amount for each of them, because they choose with a little chance among several good moves, and because now and then they make an outright mistake. Everyone except Lavi calculates just as much on a phone as on a computer, so they are equally strong wherever you play. The three strongest, Grandmaster Agnes, Ambassador Edward and Lavi, never make such mistakes, and Lavi thinks for up to two and a half seconds a move. We have tested the order between them for real: each opponent has played a series of games against the one just below, and the results are on the opponents page.
How the moves are judged
When Lavi reviews a game, every move is compared with the best move in the same position, and the difference is turned into a chance of winning. The move gets a grade by how much of that chance it cost, from a brilliant move (a sacrifice that was the best move) to a blunder. Accuracy, from 0 to 100, uses the formula Lichess publishes: moves made when a lot was at stake count for more, and a few really bad moves pull it down a lot. It can't be compared with other sites' figures, because they judge with other engines.
We have tested the grades against a much stronger engine on 100 real games from Lichess, from beginners to club players. This is how often it agrees, grade by grade:
| Grade | Right | Tested on |
|---|---|---|
| Brilliant move | 92 in 100 | 12 moves |
| Great move | 92 in 100 | 73 moves |
| Best move | 99 in 100 | 5,443 moves |
| Good move | 77 in 100 | 995 moves |
| Dubious move | 86 in 100 | 309 moves |
| Mistake | 84 in 100 | 121 moves |
| Blunder | 97 in 100 | 168 moves |
Mistakes and blunders together are right 93 times in 100. One grade we couldn't make reliable enough, the missed chance, we left out.
Puzzles, openings and statistics
The puzzles come from Lichess, the free chess site, which shares its puzzles with everyone. So do the names of the openings and the statistics on how the openings fare in real games. Thank you, Lichess!
The music and the sounds
Every sound on LaviChess was made for the house: the pieces' sounds and the theme are created in your browser. The orchestral version of the theme is built from recordings of real instruments. So are the piano, the double bass and the fiddle when the theme is played by a jazz trio or as a folk tune.
Licenses
The puzzles and the opening data from Lichess are free to use (CC0). The orchestra's instruments come from Versilian Studios Chamber Orchestra 2 Community Edition (CC0), and so do the piano, the double bass and the fiddle in the jazz trio and the folk tune. The piano was recorded by Simon Dalzell (Ivy Audio).