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Betafish - An amalgamation of AlphaZero and Stockfish.

Play it here.

Read more about it on my blog.


Betafish is a chess engine and AI move finder written in Javascript, based on the Negamax algorithm. It beats Stockfish Level 6 on Lichess, and I estimate its around 1800-2000 Elo, depending on the thinking time afforded.


  • Negamax algorithm with alpha-beta pruning
  • Move ordering using the MVV-LVA heuristic
  • Principal variation search
  • Quiescence search
  • Iterative deepening
  • Piece-square tables
  • Tapered evaluation

This enables Betafish to search to a depth of 7-8 plies and around ~1mil possible nodes, given a thinking time of around 1-2 seconds.

Possible Improvements

  • Transposition tables
  • Zobrist hashing
  • Opening tables

Of course, re-writing this in a compiled language like C++ would be a huge improvement. I wrote it in Javacript as I wanted to deploy it as a web app, as what fun would a game be without letting your friends challenge it? However, I quickly realised the limitations, as JS is definitely not suited for these computing-intensive tasks.



  • Chess Engines: A Zero to One - The article that jumpstarted my journey into chess programming.
  • WukongJS - A JS chess engine, written by Maksim Korzh, who was patient enough to answer my questions, give me pointers and point me in the right direction in this journey.
  • Bluefever Software's YouTube series - A 63-part series on chess programming, which was an absolute gold mine and served as inspiration for the bulk of the chess engine.
  • Chess Programming Wiki - A great resource for chess programming.
  • CM Chessboard - The library I used for the GUI.