Lozza

Lozza is a Javascript UCI chess engine that can be eaisly be deployed using a web worker. It can also be used with traditional chess user interfaces via Node. The source is hand-coded and easily tweaked.

Play Lozza online

• https://op12no2.github.io/lozza-ui

Play Lozza in chess user interfaces

This can be done using a batch file and full path names are recommended.

"C:\Program Files\nodejs\node.exe "c:\path\to\lozza.js"

Then use the batch file to load Lozza into the user interface. Email me if you get any problems op12no2@gmail.com.

Basic use in a browser

All you need is lozza.js from the latest release.

Here is a little example to do a 10 ply search:-

const lozza = new Worker('lozza.js');
const ucioutput = document.getElementById('ucioutput');

lozza.onmessage = function(e) {
  ucioutput.textContent += e.data + '\n'; // Lozza reponds with text as per UCI 
};

lozza.postMessage('uci');
lozza.postMessage('ucinewgame');
lozza.postMessage('position startpos');
lozza.postMessage('go depth 10');

Try this example here:-

• https://op12no2.github.io/lozza-ui/ex.htm

More examples

A sister repo has more browser-based examples for playing and analysing with Lozza.

• https://github.com/op12no2/lozza-ui

Lozza's net

Lozza's net was booted from quiet_labeled.epd and lichess-big3-resolved.epd, then iteratively improved through six generations of self play and training; initially using a diy trainer and more recently with bullet. Currently it's a simple quantised 768->(256*2)->1 squared ReLU architecture, trained on about 600M positions. It's embeded into lozza.js as a single line of code towards the end of the file.

Limitations

Lozza does not support the stop command or multi-threading.

Tweaking Lozza

You can either edit lozza.js directly or clone/download the repo and edit the individual files in src. The root of the repo has a little script b to concatenate them into lozza.js. There is also a script to do SPRT testing called sprt.

Creating your own net

Use bullet to train a 768->(N*2)->1 SqrRelu net and set NET_H1_SIZE to N in const.js. See lozza.rs for an example. Use the following command to write the weights to weights.js:-

echo "WEIGHTS_B64 = \"$(base64 -w 0 mynet.bin)\";" > src/weights.js

If you change the activation function, tweak netEval in net.js to suit.

References

• https://nodejs.org - Node
• https://www.chessprogramming.org/Main_Page - Chess programming wiki
• https://computerchess.org.uk/ccrl/4040 - CCRL rating list
• https://backscattering.de/chess/uci - UCI protocol
• https://talkchess.com - Talkchess forums
• https://discord.gg/pntchvGU - Engine Programming Discord

Acknowledgements

• https://www.chessprogramming.org/Fruit - Early versions of Lozza used a HCE based on Fruit 2.1