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Multi Variant Stockfish is a Stockfish fork specialized to play chess and some chess variants:
- Crazyhouse
- Atomic
- Horde
- King of the Hill
- Racing Kings
- Losers
- Three-Check
- Chess960 (played natively by Official Stockfish)
Multi Variant Stockfish is currently used in these lichess.org projects:
- lichess.org custom Stockfish: as engine used to play against the users on lichess.org
- fishnet: distributed Stockfish analysis for lichess.org: as engine running on contributed remote servers for games analysis on lichess.org
- PNaCl Stockfish: as engine running in Chrome browser for your personal games analysis
If you are interested to play only Chess and/or Chess960, or to play Chess and/or Chess960 at maximum strength level possible, simply use Official Stockfish. Multi Variant Stockfish, though using the same code base, is a bit slower.
The project has the goal to develop and to improve the playing strength of some chess variants not already played natively by Stockfish: patches about Chess or Chess960 will be never committed in this project.
Each patch with new idea or improvement is tested with Multi Variant Fishtest, in order to merge only code statistically proved to improve playing strength.
Once at month the maintainers routinely merge the Official Stockfish new patches and start, for each variant, a regression test:
- to check if some upstream patches are a regression for the variant
- to measure the improvement of the playing strength of the variant
Multi Variant Fishtest is a distributed tasks queue for testing new ideas and improvements for Multi Variant Stockfish, the main instance is:
http://35.161.250.236:6543/tests
Developers submit patches with new ideas and improvements, CPU contributors install a fishtest worker on their computers to play some chess games in the background to help the developers testing the patches.
The fishtest worker:
- automatically connects to the server to download: a chess opening book, the cutechess-cli chess game manager and the chess engine sources (for the actual master and for the patch with the new idea) that will be compiled according to the type of worker platform
- starts a batch of games using cutechess-cli
- uploads the games results on the server
If you are a developer, fork Multi Variant Stockfish and contribute some patches, following the instructions in Creating my first test to submit tests. You can also contribute to improve Multi Variant Fishtest, to test a patch locally on your computer simply follow Installing a development multi variant fishtest server on Ubuntu.
Even if you don't know programming yet, you can help the Multi Variant Stockfish developers to improve the chess engine by connecting your computer to the Multi Variant Fishtest following these instructions: