Endspiel

Endspiel /ˈɛnt.ʃpiːl/ n. (German)   1. the final, decisive game.   2. the final phase of a chess game.

A UCI chess engine written in Rust, with an NNUE evaluation trained from scratch on its own self-play data.

See ABOUT.md for project rationale, playing strength, and training details.

Features

• Full UCI compliance — works in any UCI GUI (Arena, CuteChess, Fritz, Banksia, Scid, …)
• NNUE evaluation (default) — HalfKP 704×32→768×2→1 SCReLU, trained from scratch on ~2.6 billion self-play positions; the net is embedded in the binary, no extra files to ship
• HCE fallback — tapered hand-crafted evaluation (UseNNUE=false) with pawn hash, mobility, king safety, pawn structure, threats, space, and endgame scaling
• Modern search — alpha-beta + PVS with iterative deepening, null move, reverse futility, futility, razoring, ProbCut, SEE pruning, LMR, IIR, singular and passed-pawn extensions, 1- and 2-ply continuation history
• Multi-threading — Lazy SMP with depth diversity (Threads UCI option)
• MultiPV — up to 256 principal variations for analysis (MultiPV UCI option)
• Syzygy tablebases — WDL probing for 3–5 man endgames via pyrrhic-rs
• Opening books — load Polyglot .bin, EPD (.epd, with bm opcodes), or PGN (.pgn) at runtime; format is auto-detected by extension
• WDL output — optional wdl W D L annotation on each info line (UCI_ShowWDL), with the win/draw/loss mapping fit per net
• Contempt and configurable time management (Move Overhead, Slow Mover)
• Performance — native-CPU release builds; on a modern desktop the engine searches in the millions of nodes per second per thread and plays competitive bullet/blitz time controls comfortably
• Cross-platform — Linux x86_64/ARM64, Windows x86_64/ARM64, macOS Apple Silicon
• Self-contained binary — no runtime dependencies, no external net file

Download

Prebuilt binaries are on the Releases page:

Platform	Binary	ISA / notes
Linux x86_64 (recommended)	endspiel-linux-x64	AVX2 / x86-64-v3, PGO-optimised
Linux x86_64 (AVX-512)	endspiel-linux-x64-avx512	x86-64-v4 — faster on Zen 4/5, Sapphire Rapids, etc.
Windows x86_64 (recommended)	endspiel-win-x64.exe	AVX2 / x86-64-v3, PGO-optimised
Windows x86_64 (AVX-512)	endspiel-win-x64-avx512.exe	x86-64-v4 — faster on CPUs with AVX-512
Windows ARM64	endspiel-win-arm64.exe	generic ARM64
macOS Apple Silicon	endspiel-mac-arm64	apple-m1, PGO-optimised
Raspberry Pi 5	endspiel-linux-arm64-pi5	cortex-a76, PGO-optimised; requires Pi OS Trixie (glibc ≥ 2.39)

Picking a build. The recommended (-v3) builds run on essentially any CPU sold in the last decade and are profile-guided-optimised for ~5–15% extra throughput. If your CPU has AVX-512 (AMD Zen 4/5, recent Intel Xeon, etc.), the -avx512 build is typically 30–60% faster on NNUE evaluation but will refuse to run on older hardware (illegal-instruction crash). When in doubt, use the recommended build.

Raspberry Pi 5. Any RAM tier runs the engine; hash size is the only thing that scales with it. Set Hash in your GUI rather than relying on the 256 MB default:

Pi 5 RAM	Recommended Hash	Notes
4 GB	512–1024 MB	usable for blitz/rapid; leave ≥2 GB for the desktop/browser
8 GB	2048–4096 MB	sweet spot — full Pi-5 strength at all time controls
16 GB	4096–8192 MB	only worth it for deep analysis or running other workloads alongside

Expect NPS roughly 5–10× lower than a modern x86 desktop, so plan for a noticeable Elo drop at fixed time controls and compensate by giving the engine more thinking time. Active cooling is recommended: under sustained engine load the SoC will thermally throttle without a fan.

Usage

Endspiel is a command-line program used through a UCI-compatible chess GUI (Arena, CuteChess, Fritz, Banksia, etc.). Point the GUI at the binary — no further setup is required.

Bench — runs a fixed-depth search across a small set of positions and prints the total node count, elapsed time, and NPS. Useful as a sanity check that the binary runs end-to-end:

./endspiel bench          # default depth 14
./endspiel bench 18       # deeper, for performance tuning

macOS users — run this once from a terminal before pointing a chess GUI at the binary. The release binaries are not code-signed, so macOS Gatekeeper will quarantine them. If that's the case, this command surfaces the error clearly instead of leaving the GUI to silently fail to launch the engine. To clear the quarantine flag:

chmod +x endspiel-mac-arm64
xattr -d com.apple.quarantine endspiel-mac-arm64

Then re-run ./endspiel-mac-arm64 bench — once you get a Nodes/NPS line, the GUI will also be able to launch it.

UCI Options

Option	Default	Description
Hash	256	Transposition table size in MB
Threads	min(available, 16)	Search threads
Move Overhead	20	Time safety margin in ms
Slow Mover	100	Time usage scaling (%) — >100 thinks longer, <100 plays faster
Contempt	20	Draw avoidance in centipawns
SingularExt	1	Singular extension: 0 = off, 1 = conservative, 2 = aggressive
UseNNUE	true	Use NNUE evaluation; false falls back to HCE
EvalFile	(embedded)	Path to an external .nnue / quantised.bin net
BookFile	(disabled)	Path to an opening book: Polyglot .bin, EPD .epd, or PGN .pgn (auto-detected by extension)
SyzygyPath	(disabled)	Path to Syzygy tablebase directory
MultiPV	1	Number of principal variations to report (1–256)
UCI_ShowWDL	false	Append wdl <win> <draw> <loss> (0–1000) to each info line

Set BookFile or SyzygyPath to a valid path to enable; clear to disable. No separate toggle is needed.

Notes

• Hash — increase for long time controls or analysis; watch hashfull in engine output (permille, so 950 = 95%).
• Threads — Lazy SMP; scaling is sub-linear. Stick to physical core count.
• EvalFile — load an alternate net at runtime without rebuilding. Clear to revert to the embedded net.
• SyzygyPath — WDL probing for 3–5 man endgames. Multiple directories: : on Linux/macOS, ; on Windows.

Fritz 20 (Windows): Fritz manages Syzygy and opening books through its own systems. Set the tablebase path in Fritz's settings — it forwards it to Endspiel automatically. To let Endspiel use its own BookFile, disable Fritz's opening book in the match settings. Verify loading via View → Engine Output: a successful load prints info string BookFile loaded from '...'.

Build from Source

Requires Rust 1.95.0+.

cargo build --release
# binary: target/release/endspiel

License

GPL-3.0-or-later — see LICENSE.