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DriftWood

DriftWood

A chess engine with a built-in web UI. Play in your browser, no setup beyond one binary.

Quick Start · Play Now · Internals · Contribute

C++17 MIT License Tests Platform

A ~2400 ELO chess engine written in C++17. Single binary, no dependencies, no internet required. Built-in web UI with drag-and-drop play, clock, move history, and live eval. Connect it to any UCI GUI. Multi-threaded search, Syzygy tablebases, opening book, the works.

Why another chess engine? Most serious engines are CLI-only and require a separate GUI. DriftWood ships one binary that speaks UCI, has a web UI baked in, and has a clean enough codebase to read, learn from, and hack on.

graph TB
    subgraph "driftwood (single binary)"
        UI["Web UI<br/>chessboard.js + chess.js"]
        HTTP["HTTP Server<br/>cpp-httplib"]
        UCI["UCI Protocol"]
        SEARCH["Searcher<br/>PVS + Lazy SMP"]
        EVAL["Evaluation"]
        TT["Transposition Table"]
        BOOK["Opening Book"]
        SYZYGY["Syzygy Tablebases"]
        BOARD["Board<br/>bitboards + Zobrist"]
        MOVEGEN["Move Generation<br/>magic bitboards"]
    end

    UI <-->|REST API| HTTP
    UCI <--> SEARCH
    HTTP --> SEARCH
    SEARCH --> EVAL
    SEARCH --> TT
    SEARCH --> BOOK
    SEARCH --> SYZYGY
    EVAL --> BOARD
    SEARCH --> BOARD
    BOARD --> MOVEGEN

    style UI fill:#2d3748,stroke:#718096,color:#e2e8f0
    style HTTP fill:#2d3748,stroke:#718096,color:#e2e8f0
    style UCI fill:#2d3748,stroke:#718096,color:#e2e8f0
    style SEARCH fill:#2b6cb0,stroke:#3182ce,color:#fff
    style EVAL fill:#2b6cb0,stroke:#3182ce,color:#fff
    style TT fill:#2f855a,stroke:#38a169,color:#fff
    style BOOK fill:#2f855a,stroke:#38a169,color:#fff
    style SYZYGY fill:#2f855a,stroke:#38a169,color:#fff
    style BOARD fill:#744210,stroke:#d69e2e,color:#fff
    style MOVEGEN fill:#744210,stroke:#d69e2e,color:#fff
Loading

Play Now

git clone https://github.com/akorite/driftwood.git
cd driftwood
cmake -B build -S . -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)
./build/driftwood serve

Open http://localhost:8080, pick a side, play.

Gameplay

Web UI Features
Drag-and-drop with legal move indicators Clock with 1 / 3 / 10 / 30 minute presets
Move history in SAN (click to jump back) Captured pieces display
Live evaluation + depth readout Board flip (F), new game (N)

Everything is vendored under web/vendor/. Works fully offline, no CDN, no npm install.

Engine Internals

DriftWood is a real chess engine, not a toy. It has the search techniques you'd find in competitive engines, implemented in ~4K lines of readable C++17.

Search

flowchart TD
    ID["Iterative Deepening<br/>depth 1, 2, 3, ..."]
    AW["Aspiration Window<br/>narrow search first"]
    PVS["PVS: Search root move"]
    ORDER["Move Ordering<br/>TT hash > MVV-LVA > Killers > History"]
    PRUNE{"Pruning checks"}
    LMR["LMR: reduce late moves"]
    NMP["Null-Move: skip side, search reduced"]
    FUTILITY["Futility: prune at frontier"]
    RAZOR["Razoring: drop to qsearch"]
    EXTEND["Check Extension: +1 ply"]
    QS["Quiescence Search<br/>captures only, stand-pat"]
    STORE["Store in TT"]
    NEXT{"More moves?"}
    DEEPER{"time_up?"}

    ID --> AW --> PVS --> ORDER --> PRUNE
    PRUNE -->|quiet + low depth| LMR
    PRUNE -->|non-endgame| NMP
    PRUNE -->|frontier, eval < alpha| FUTILITY
    PRUNE -->|very low depth| RAZOR
    PRUNE -->|in check| EXTEND
    LMR --> NEXT
    NMP --> NEXT
    FUTILITY --> NEXT
    RAZOR --> QS --> NEXT
    EXTEND --> PVS
    NEXT -->|yes| PVS
    NEXT -->|no| STORE --> DEEPER
    DEEPER -->|no| ID
    DEEPER -->|yes| DONE["Return best move"]

    style ID fill:#2b6cb0,stroke:#3182ce,color:#fff
    style PVS fill:#2b6cb0,stroke:#3182ce,color:#fff
    style QS fill:#2b6cb0,stroke:#3182ce,color:#fff
    style PRUNE fill:#c53030,stroke:#e53e3e,color:#fff
    style LMR fill:#744210,stroke:#d69e2e,color:#fff
    style NMP fill:#744210,stroke:#d69e2e,color:#fff
    style FUTILITY fill:#744210,stroke:#d69e2e,color:#fff
    style RAZOR fill:#744210,stroke:#d69e2e,color:#fff
    style EXTEND fill:#2f855a,stroke:#38a169,color:#fff
    style STORE fill:#2f855a,stroke:#38a169,color:#fff
Loading

Evaluation

  • Material + piece-square tables with middlegame/endgame interpolation
  • Mobility (N, B, R, Q), king safety (pawn shield, attacker weights)
  • Pawn structure: doubled, isolated, passed, backward, candidates
  • Knight outposts, bishop pair, rook on 7th, space, threats
  • Passed pawn king proximity

Threading

flowchart LR
    subgraph shared["Shared State"]
        TT["Transposition Table<br/>(1-1024 MB)"]
    end

    subgraph t0["Thread 0"]
        H0["History"]
        K0["Killers"]
        C0["Countermove"]
    end

    subgraph t1["Thread 1"]
        H1["History"]
        K1["Killers"]
        C1["Countermove"]
    end

    subgraph tN["Thread N"]
        HN["History"]
        KN["Killers"]
        CN["Countermove"]
    end

    t0 <-->|read/write| TT
    t1 <-->|read/write| TT
    tN <-->|read/write| TT

    style shared fill:#2f855a,stroke:#38a169,color:#fff
    style TT fill:#2b6cb0,stroke:#3182ce,color:#fff
    style t0 fill:#2d3748,stroke:#718096,color:#e2e8f0
    style t1 fill:#2d3748,stroke:#718096,color:#e2e8f0
    style tN fill:#2d3748,stroke:#718096,color:#e2e8f0
Loading

Lazy SMP: multiple threads share one transposition table, each with private history/killers/countermover. Thread count configurable via UCI (setoption name Threads value 4).

Extras

  • Opening book: 321 entries, weighted random selection
  • Syzygy tablebases: WDL/DTZ probing for 6-7 man endgames
  • Time management: adaptive budgeting per clock tier, depth caps per budget

UCI Options

Option Type Default Description
Hash spin 64 Transposition table size (MB)
Threads spin 1 Search threads
SyzygyPath string Path to Syzygy tablebase files
BookFile string books/driftwood.bin Opening book path
BookMoves spin 12 Maximum book moves

HTTP API

The web UI is backed by a simple REST API. Use it to build your own frontends or integrate DriftWood into anything.

Method Endpoint Description
GET /api/new_game?color=white|black|random Start a new game
POST /api/move Send a move, get engine reply
GET /api/state?fen=<FEN> Legal moves, check/mate status
GET /api/eval?fen=<FEN>&depth=N Evaluation with PV line

CLI

./build/driftwood                    # UCI mode (default)
./build/driftwood serve [port]       # Web UI on :8080
./build/driftwood perft 5            # Move generator verification
./build/driftwood bench 12           # Benchmark (nodes/sec)
./build/driftwood selfplay 20        # Engine vs. itself

Tests

cd build && ctest --output-on-failure

54+ tests covering move generation, evaluation correctness, search tactics, TT behavior, Lazy SMP determinism, and SEE.

Building

cmake -B build -S . -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)

Requirements: C++17 (GCC 9+ / Clang 10+ / MSVC 2019+), CMake 3.16+. That's it. No Boost, no external libs. GoogleTest is fetched automatically for the test suite.

Cross-platform:

  • Linux / macOS: gcc / clang
  • Windows: MSVC or MinGW

Contributing

Contributions welcome. Bug fixes, evaluation tuning, new pruning ideas, test positions, docs.

See CONTRIBUTING.md for setup, code style, and PR checklist. Open an issue or discussion before large changes.

License

MIT

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A from-scratch C++17 chess engine with embedded web server and Lichess-like UI

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