Coco is an autonomous tournament-grade C++20 chess engine pairing custom 768→512×2 NNUE neural evaluation with razor-sharp alpha-beta search and Lazy SMP concurrency.
Conceived, architected, and maintained by NotKaede-11. Free and open source under GPL-3.0.
Every module in Coco is designed in modern C++20 with cache locality, zero dynamic allocation during search, and vector SIMD intrinsics.
A dual-perspective neural network architecture transforming board squares into dual 512-dimension accumulators with clipped ReLU activations. Incrementally updated on every move.
Principal Variation Search with iterative deepening, adaptive aspiration windows, Late Move Reductions (LMR), Singular Extensions, and Reverse Futility Pruning.
64-bit Bitboard representations for all piece topologies. Sliding attack masks for rooks and bishops are computed in O(1) time using precomputed Magic Hash tables.
Multi-threaded scaling via lockless shared Transposition Tables across all worker threads. Seamless endgame resolution via Syzygy 3-4-5-6 piece WDL and DTZ probing.
Every Coco release binary includes the complete 768→512×2 neural network compiled directly into the executable. There are no separate .nnue weight files to download, locate, or configure.
Load the Coco binary directly into Cutechess, BanksiaGUI, Nibbler, or Arena. The engine immediately boots into full NNUE mode with zero missing-file errors.
Unlike engines that silently degrade to Handcrafted Evaluation (HCE) when missing weight files, Coco guarantees 100% neural evaluation by default in every tournament game.
Engine researchers and neural network trainers can still benchmark custom experimental weights anytime via the standard UCI EvalFile option.
Precompiled standalone binaries ready to be loaded into Cutechess, BanksiaGUI, Nibbler, Arena, or any standard UCI chess interface.
Coco Chess Engine was created and is independently developed by NotKaede-11 as an ambitious study in modern chess programming, low-latency SIMD evaluation, and autonomous neural training pipelines.
Named after Coco from Witch Hat Atelier—built with that same spirit of quiet discovery and disciplined craft. Coco Chess Engine and CuckooChess are different projects. The engine is developed completely in the open, validated through continuous CCRL tournament testing, and published under the GNU General Public License v3.0.