TinyChessDuck: A 969 Tokens C# Chess Bot

• This is a chess bot I wrote in a single 969-tokens C# file as part of youtuber Sebastian Lague's Chess Coding Challenge.
• The challenge was: Given a chess framework, implement a chess AI under the limit of 1024 tokens only to battle it out against other participants' bots.
• Overall, I enjoyed participating very much, I learned a lot about chess programming, search algorithms and evaluation heuristics, and my bot did surprisingly well in the tournament (see results).

Table of Contents

• Objective
• The AI
• Results
• Try It
• Credits

Objective

The objective of this challenge was to implement strong chess search and evaluation algorithms in a maximum of 1024 tokens of code, without the overhead of writing an entire chess framework. This limit was (probably) enforced for 2 reasons:

• Preventing participants from copying code from famous open source chess engines (for example: Stockfish)
• Encouraging participants to come up with creative ways of writing tiny chess AI algorithms, for example:
  • Designing compression/encoding algorithms for big amounts of values like piece square tables
  • Choosing between multiple search extension algorithms, pruning techniques and evaluation parameters (you can't fit'em all in 1024 tokens!)

I learned a lot about chess AI programming and I got a chance to apply my problem-solving techniques to overcome the token-limit problem, like:

• Using bit-manipulation to compress piece square tables (768 tokens) into 64-bit ulongs (96 tokens)
• Using basic search algorithms like minimax and alpha-beta pruning
• Using dynamic programming techniques in transposition tables to reduce search time

The AI

Most chess bots consist of a Search function and an Evaluation function.

• My Search function:

  • Minimax search and alpha-beta pruning inside a negamax framework
  • Quiescence search

• My Evaluation function:

  • Piece square tables only evalution

• Techniques to reduce search time:

  • Most-valuable-victim - least-valuable-aggressor move ordering
  • Iterative deepening framework

Results

My bot ranked 117th out of 624 bots, sadly - but understandably - it wasn't mentioned in Sebastian's results video. Here is a screenshot from the video:

Tournament games played by all bots were published to this repo, I wrote a simple Python script to extract my bot's 64 games out of all games and analyze basic stats like wins/losses and color. Here are the results:

Try It

• If you just want to play against the bot, download and run the executable from here
• If you want to run the project in your IDE, you must have .NET 6.0, download the source code and open Chess-Challenge.sln

Credits

• Sebastian Lague
  • Organized the challenge, wrote the entire chess framework and its documentation
• Chess coding discord community
  • Helped with code and guides, especially users selenaut and jw1912 for open-sourcing their code
• Chess programming wiki
  • Very good hub of chess programming knowledge
• Yours truly
  • Wrote MyBot.cs and PackingPST.cs