Open Source & Corresponding Source

Chess Coach · last updated 2026-07-21

Chess Coach is built on open-source software. This page provides the required attribution for the components we use and, for the GPLv3-licensed chess engines that the Android app distributes on-device, the Corresponding Source as required by section 6 of the GNU General Public License, version 3.

How to get the source. For each GPL engine below we give the exact upstream version tag plus the complete build instructions we used to produce the binary shipped in the app. Together these constitute the Corresponding Source. This page is kept available for as long as Chess Coach distributes the corresponding binary. If any upstream link is unavailable, contact us (see the bottom of this page) and we will provide the source directly.

1. GPLv3 engines shipped on Android (on-device)

Stockfish 18 — GPL-3.0-or-later

The Android app bundles the official, unmodified Stockfish 18 binary for arm64-v8a (release tag sf_18), placed at app/src/main/jniLibs/arm64-v8a/libstockfish.so. Because it is the official release binary with no modifications, its Corresponding Source is the upstream source at the same tag:

Copyright © The Stockfish developers (see the AUTHORS file in the source).

Leela Chess Zero (lc0) v0.31.2 — GPL-3.0-or-later

The "human-like bots" (Maia) run on an lc0 binary that we cross-compile ourselves for arm64-v8a from tag v0.31.2, placed at app/src/main/jniLibs/arm64-v8a/liblc0.so (no embedded network). Because this is a self-built binary, the Corresponding Source comprises the upstream lc0 source, the statically-linked OpenBLAS source, and the exact build configuration below.

Exact build steps (the complete build script is documentos/maia/build-lc0-android.sh in our source tree; its essential commands are reproduced here so the binary can be regenerated from upstream alone):

# 1) OpenBLAS v0.3.27, static, android-aarch64
git clone --depth 1 -b v0.3.27 https://github.com/OpenMathLib/OpenBLAS.git
make -C OpenBLAS TARGET=ARMV8 ONLY_CBLAS=1 NO_LAPACK=1 NO_SHARED=1 \
     USE_OPENMP=0 USE_THREAD=0 HOSTCC=cc \
     CC=aarch64-linux-android21-clang AR=llvm-ar RANLIB=llvm-ranlib
make -C OpenBLAS PREFIX=<install> NO_SHARED=1 install

# 2) lc0 v0.31.2 with submodules
git clone --depth 1 -b v0.31.2 --recurse-submodules \
     https://github.com/LeelaChessZero/lc0.git

# 3) meson cross-file (NDK 26, 16 KB page alignment for Android 15+)
#   [host_machine] system=android cpu_family=aarch64 cpu=aarch64 endian=little
#   [properties]  cpp_link_args = ['-llog','-static-libstdc++','-Wl,-z,max-page-size=16384']
#   [binaries]    c/cpp = aarch64-linux-android21-clang(++), ar/strip/ranlib = llvm-*

# 4) configure + build
meson setup arm64-v8a --buildtype release \
     -Dgtest=false -Dembed=false -Ddefault_library=static \
     -Dopenblas=true -Dopenblas_include=<install>/include \
     -Dopenblas_libdirs=<install>/lib --cross-file crossfile-aarch64
ninja -C arm64-v8a lc0
llvm-strip arm64-v8a/lc0   # → liblc0.so

Copyright © The LCZero Authors (lc0) and © The OpenBLAS contributors (OpenBLAS, BSD-3-Clause).

Maia networks (weights) — data

The nine Maia strength networks (maia-1100 … maia-1900) are shipped as data (neural-network weights loaded by lc0 at runtime), not as executable code. They originate from the Maia Chess project: github.com/CSSLab/maia-chess (CSSLab, University of Toronto). Maia-1 networks are distributed under GPL-3.0.

2. iOS build

The iOS app does not ship any GPL binary on-device. Stockfish runs server-side (accessed over the network, which is not "conveying" under the GPLv3); on-device play and analysis use Caissa (MIT), and the human-like play uses a clean-room ONNX Runtime (MIT) with MIT-licensed models. Section 6 therefore does not apply to the iOS build; only attribution applies (section 3 below).

3. Other components & attributions

4. Full license texts

BSD-3-Clause notice — chess piece graphics

Copyright (c) 2006, Colin M.L. Burnett
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.
3. Neither the name of the copyright holder nor the names of its contributors
   may be used to endorse or promote products derived from this software
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

MIT License — Celtic, Spatial and Fantasy piece sets

MIT License

Copyright (c) Maurizio Monge

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Contact

For any question about these licenses or to request the Corresponding Source directly, email juanfranj80@gmail.com.

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