Brass Pawn is licensed under the GNU Affero General Public License, version 3. The complete corresponding source code is published at https://github.com/minchopm/chess-trainer. You may use, study, modify and redistribute it under those terms.

Why AGPLv3

The app includes two engines. Stockfish is licensed under the GNU General Public License version 3. Reckless is licensed under the GNU Affero General Public License version 3. Both are copyleft: a work that includes either and is distributed must be distributed under the same terms.

Both are compiled into and linked with the application, so both obligations apply at once. Section 13 of the GPLv3 exists for exactly this case — it permits combining GPLv3 code with AGPLv3 code — and it says the Affero requirement governs the combined work. So the whole application carries AGPLv3. This is not a footnote we discovered late; it is the condition of using engines this strong, and it is a fair one.

The Affero clause is the difference between the two licences: it extends the obligation to publish source from distributing a program to letting people use it over a network. It changes nothing about how this app behaves. Both engines run on your device, and nobody interacts with them remotely: the only thing the app fetches from us is the day’s games for its Today screen, a static file. The source is published either way.

Two things follow, and both are worth knowing before you buy anything.
You get the source. Not a marketing gesture — a licence obligation, and your right. The repository holds the iOS app, the Swift rules engine, the training logic, the puzzle-mining pipeline and this website.
There will never be advertising in it. A proprietary advertising SDK compiled into the same binary would make the combined work undistributable under either licence. Selling the app is fine — copyleft has never forbidden charging — but bolting a closed SDK onto it is not.

Stockfish

Copyright © 2004–2026 The Stockfish developers (see the project’s AUTHORS file)
Licensed under the GNU General Public License version 3
Upstream: github.com/official-stockfish/Stockfish
Modifications: none. The engine source is vendored unchanged. The only added file is a small C interface over its public Engine class, written for this project and licensed under GPLv3 along with the rest.

The two NNUE evaluation files are produced by the Stockfish project and distributed under the same licence. They are not committed to the repository; a script fetches the exact versions the bundled engine expects.

Brass Pawn is not affiliated with or endorsed by the Stockfish project. Stockfish is used under the terms of its licence, and it is named here — prominently, on its own page — because that is what those terms and ordinary decency both ask for.

Reckless

Copyright © its authors (see the project’s repository)
Licensed under the GNU Affero General Public License version 3
Upstream: github.com/codedeliveryservice/Reckless
Modifications: three, all listed. The engine source is otherwise vendored unchanged. src/ffi.rs is a new file — a C interface over the engine, written for this project, and needed because the crate exports nothing usable: every module in src/lib.rs is private, so nothing outside it can reach the search. src/lib.rs gains one line declaring that module, and Cargo.toml gains staticlib to its crate types so it can be linked into an application. All three are licensed under AGPLv3 along with the engine.

Its evaluation network is compiled into the engine binary rather than fetched, so there is no separate weights file and nothing to download.

Brass Pawn is not affiliated with or endorsed by the Reckless project. It is used under the terms of its licence, and named here for the same reasons Stockfish is.

Lichess

Most of the bundled tactics puzzles come from the Lichess puzzle database, and the games behind Guess the Elo come from the Lichess game archives. Both are released into the public domain under CC0 1.0.

No attribution is required by that licence. It is given here because it is deserved: those 14,185 puzzles carry ratings calibrated against millions of real solving attempts, which is something no amount of local computation could produce.

Brass Pawn is not affiliated with or endorsed by Lichess. The bundled games keep the two players’ ratings and moves, and not their usernames.

Every component

Third-party components and their licences
Component	What it does	Licence
Stockfish The Stockfish developers, 2004–2026	The chess engine. Search, evaluation and the NNUE networks — the whole coach.	GNU GPL v3
Reckless The Reckless authors	The second chess engine. Its evaluation network is compiled into it, so there is no separate weights file.	GNU AGPL v3
Stockfish NNUE networks The Stockfish project	The two neural network evaluation files the bundled engine expects.	GNU GPL v3
Published game collections The moves are matters of record	900 game scores for Watch, from published collections of the players’ own games. Scores only — no annotations are included.	Not copyrightable (records of play)
Lichess puzzle database Lichess	14,185 of the bundled tactics puzzles, with human-calibrated ratings and themes.	CC0 1.0 (public domain)
Lichess game archives Lichess	1,624 rated games, for Guess the Elo. Usernames are not kept.	CC0 1.0 (public domain)
chess.js Jeff Hlywa	Used by the project’s build tooling only. It is not in the iOS app.	BSD 2-Clause
GameKit Apple Inc.	Apple’s framework, used for online matchmaking and to carry moves.	Apple SDK terms
Three.js three.js authors	This website only — the title sequence on the front page.	MIT
Angular Google LLC and contributors	This website only.	MIT

Getting the source

The complete corresponding source for the version you are running is at https://github.com/minchopm/chess-trainer, tagged by release. If you would rather have it another way — a tarball, a physical medium, a copy of a specific tag — write to support@brasspawn.com and you will get it. That offer is part of the licence, not a courtesy.

Names and marks

“Brass Pawn”, the wordmark and the app icon are ours and are not covered by the AGPL. You may redistribute modified versions of the software — that is the point of the licence — but not under our name or marks in a way that suggests they came from us.

Apple, App Store, iPhone, iPad and Game Center are trademarks of Apple Inc. This app is not affiliated with, sponsored by or endorsed by Apple.

Licences & attribution