Yakka is a Chess Engine written in object pascal (Delphi) that implements the Universal Chess Interface (UCI) protocol.

• Windows 11 x64 Platform
• Command-line, Console Application
• Written in Delphi Object Pascal
• Will run on x86-64 CPU's which support BMI2 and AVX2 instruction set

Yakka implements the Universal Chess Interface (UCI) protocol that is compatible with most popular Chess GUIs.

It is recommended to use a Chess GUI application such as Arena, BanksiaGUI or Cute Chess.

Alternatively Yakka can be run as a command line console using UCI commands.

• option name Threads type spin default 1 min 1 max 16
• option name Hash type spin default 64 min 1 max 256
• option name Clear Hash type button
• option name Ponder type check default false
• option name OwnBook type check default false
• option name UCI_EngineAbout type string

You can download the precompiled Windows executable : 'Yakka v1.5 x64.exe'. This will run on x86-64 CPU's which support the BMI2 and AVX2 instruction sets.

I currently can't provide a LINUX executable, but will investigate this possibility for a future release.

To build the engine from source, use Delphi 12.0 Alexandra or later version.

• Import the source files from GitHub repository

• Set Target Platform to Windows 64-bit

• Open Project Resources and Images..., add the following to Resource Files:

  • File Name: Opening_Book_00.txt
  • Type: RCDATA
  • Identifier: Open_Book
    +
  • File Name: NNUE 768→512x2→1 501451147c +50+ gen8 b6.net
  • Type: RCDATA
  • Identifier: _768x512_x2_gen8_b6

• Build Yakka

• Board Representation and Move Generation

  • Bitboard based
  • Make/Unmake
  • Fully legal move generation
  • uses PEXT / PDEP instructions (requires BMI2) for sliding move generation

• Search

  • ABDADA parallel search (supports up to 16 search threads)
  • Negamax search with Alpha-Beta pruning
  • Principal Variation Search (PVS)
  • Aspiration windows
  • Iterative deepening
  • Quiescence Search (QS)
  • Transposition table (two buckets with aging)
  • Singular Extension

• Selectivity

  • Reverse futility pruning
  • Recursive null-move forward pruning
  • Enhanced forward pruning
  • Enhanced Transposition Cut-off (ETC)
  • Internal Iterative Deepening (IID)
  • Late Move Reduction (LMR)
  • Late Move Pruning

• Move Ordering

  • Hash move
  • Captures (MVV/LVA)
  • Static Exchange Evaluation (SEE)
  • Killer moves
  • Counter move
  • History heuristic

• Evaluation

  • NNUE net 768>512x2>1 (requires AVX2)

• Opening Book

  • Own internal format
  • Total Book Positions = 8507 (v1.1)
  • Total Book Moves = 12184 (v1.1)

• Yakka v1.0 - 10th April 2024 Initial release
• Yakka v1.1 - 15th September 2024 Bug fixes and improved playing strength
• Yakka v1.2 - 8th February 2025 Changed evaluation from HCE to NNUE
• Yakka v1.3 - 10th August 2025 Bug fixes, implemented pondering and improved NNUE implementation
• Yakka v1.4 - 11th November 2025 Bug fixes and improved NNUE implementation
• Yakka v1.5 - 22nd January 2026 Strength gain using larger NNUE net and output buckets

Tested on desktop with Intel Core i9-9900K CPU @ 3.60GHz, Windows 11 x64, using 'Cutechess-cli'

Please let me know of any bugs, compilation-problems or stability issues. Any ideas, comments or suggestions for improvement are always welcome.

This project is licenced under the MIT Licence

In no particular order:

• Much experimenting / tweaking
• MultiPV
• Endgame Tablebases