What is Leela Chess Zero?

Leela Chess Zero (short Lc0 or Leela) is a free open source chess engine based on neural networks. Lc0 was developed from the Go engine Leela Zero Go, which in turn was developed from the research results of AlphaGo Zero by Google DeepMind. Through this model, Leela is able to learn chess without being taught by humans. Leela starts with only knowing the rules of chess and increases her playing strength with reinforcing learning by constantly playing against herself.

It is difficult to determine an Elo figure for Leela, as the playing strength increases with each additional game against itself. But Leela is also at a similar level to Stockfish 15 and Komodo 3 in 2022, the two leading chess programmes.

Leela Chess Zero and AlphaZero

One of the main reasons for the development of Leela Chess Zero is to improve the functioning of AlphaZero to confirm. After AlphaZero significantly beat the previously leading chess program Stockfish 8 in 2017, an uproar went through the chess community. AlphaZero's new approach of not relying on a human-generated database of countless moves and plays, as with Stockfishbut mastering chess through knowledge of the rules and self-play alone was a completely new approach. The AlphaZero project was discontinued a short time later, but continued in some form through Leela Chess Zero. The code of AlphaZero is still a secret today, but an ambitious community of developers around Gary Linscott managed to create Leela based on its model. By the way, there is no official game by Leela and AlphaZero.

Leela Chess Zero and Stockfish

Stockfish is the world's leading chess engine and, like Lc0, can be used free of charge as open source. The decisive difference between the two, apart from their approach to chess, also lies in the different nature of the engine itself. While Stockfish is a "classic" engine with enormous computing power, Leela is a Artificial intelligence with neural networks. Since Stockfish 12, it has combined the strengths of both programmes and also uses the Efficiently Updatable Neural Network (NNUE) for positional evaluation, greatly improving its performance. Today, Stockfish 15 is one of the best chess engines in the world.

Leela Chess Zero and Stockfish play regular matches against each other, the majority of which Stockfish wins. But Leela's playing strength is getting closer and closer to Stockfish, and in 2021 it was the second best chess program, behind Stockfish 14.

Online resources

Leela can be with GitHub as an open source engine free of charge. Since Lc0 is not a complete chess program but a Universal Chess Interface (UCI), a graphical user interface (GUI) is also required. Popular GUIs are for example Chessbase, Cutechess, Nibbler or BanksiaGUI. Another possibility to play against Leela are the Lichess bots. No additional programme needs to be downloaded to play. At https://lichess.org/team/all-the-leelas are the bots Lc0Test, leela2200 or MiniHuman, which are almost always online. The Maia bots are also under https://lichess.org/player/bots available to play.