Lavi is the chess engine behind LaviChess and its Swedish sister Schackdags. We built him from scratch: the rules, the search, and the net that judges positions. The net learned from games Lavi played against himself. He is also the strongest player in the house. When you play Lavi, the engine plays at full strength, in your own browser.
Play Lavi
- Play against Lavi. Full strength, free, no account.
- Review your games. Paste in a game, and Lavi grades every move.
- Twenty-five opponents. From Doris the Cat, who moves at random, to Lavi himself. Most of them think with Lavi, but less, and each with a taste of their own.
- The daily puzzle. A new one every day, the same for everyone.
- Play a person. Someone waiting with the same time control.
In short
| Version | Lavi 4, since November 12, 2026 |
|---|---|
| Made by | John Tibell, Tentmaker Sweden |
| Protocol | UCI |
| Written in | Rust, from scratch |
| Search | Principal variation search with iterative deepening, aspiration windows and a transposition table. On top of that the well-known refinements, among them null move, late move reductions, singular extensions, ProbCut, and history and correction tables. |
| Judgement | A neural net: 768 inputs, 512 neurons for each side's view, 8 output buckets. It learned from about 754 million positions from Lavi's own games. |
| Threads | One |
| Source | Closed. Lavi is a commercial product. |
Rating lists
We are sending Lavi 4 to CCRL, the Computer Chess Rating Lists. Its testers play engines against each other under the same conditions, on their own computers, and publish every game. Their rating will stand here as soon as they have one.
Download Lavi
Lavi 4 for Windows, 64-bit, for processors with AVX2, with the net built in. Load the file in any chess program that speaks UCI. One thread, and 256 MB of hash unless you set another size.
Download Lavi 4 zip, 0.8 MB
Windows may ask before it runs the file the first time, because the file isn't signed yet.
The terms in short (the license in the zip file is what applies):
- Free to use: play against Lavi, analyse with him, test him, and publish your results and games.
- Please don't share the file. Link to this page instead, where the latest version always is.
- Lavi may not be built into other software or offered to others as a service.
Testing Lavi for a rating list? We'd love to hear from you: hello@lavichess.com.
Who makes Lavi?
Lavi is made by John Tibell at Tentmaker Sweden, the company behind LaviChess and Schackdags. The ideas in his search are well known in computer chess. Many programmers have shared them over many years, and we thank them. The code, the net and the games it learned from are our own. Lavi was built with the help of AI.
Strength and versions
How strong is Lavi?
We state it as a test, not as a rating. On November 12, 2026, Lavi 4 played 800 games against the chess program Stockfish 19, set to its strength 3190. Each side had ten seconds for the whole game, plus a tenth of a second for every move. Both programs ran directly on an ordinary home computer with an AMD Ryzen 7 5700G processor, fourteen games at a time. Lavi won 344 games and lost 191, and 265 were drawn.
3190 is a setting on Stockfish's own scale, not a human rating. The games started from short, randomly chosen openings, and each opening was played twice with the colors swapped. Here on the site Lavi calculates in your browser, which is slower than running directly on the computer; by how much depends on your computer or phone.
Lavi's versions
Lavi gets a new number each time we change how he plays. The number is shown under the review of a game, and in the PGN file of your games against Lavi from Lavi 2 on.
| Version | Since | What's new |
|---|---|---|
| Lavi 4 | November 12, 2026 | He searches more wisely and remembers: five improvements in how he searches, among them that he now remembers what he has learned from move to move in the same game. The part that judges positions learned from 330 million more positions of Lavi 3's games. Against Lavi 3 he won 191 games and lost 85, and 524 were drawn. |
| Lavi 3 | November 10, 2026 | He searches more wisely: three improvements in how he chooses which moves to look at more closely. The part that judges positions learned from 83 million more positions of Lavi 2's games. Against Lavi 2 he won 186 games and lost 98, and 516 were drawn. |
| Lavi 2 | November 8, 2026 | The part that judges positions is twice the size and learned from 341 million positions of his own games. He calculates a little slower but judges better. |
| Lavi 1 | November 5, 2026 | The first: our own engine, built from scratch. The part that judges positions learned by playing against itself. |