Licences and notices
The checker
MIT licence:
MIT License Copyright (c) 2026 Problem Forge, LLC 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.
The site's own code
Copyright (C) 2026 Problem Forge, LLC. All rights reserved. The JavaScript and CSS served by this site are served, not licensed, except the checker (above).
Instances and answers
The files this site gives out (your own copies, the guest samples, the bounty instance) and the answers given out are dedicated to the public domain under CC0 1.0 Universal. Use them for anything; no attribution required.
Third-party components
On the server: the GNU C++ standard library (GPL-3.0 with the GCC Runtime Library Exception), Boost (Boost Software License 1.0: Asio, Beast, JSON), OpenSSL 3 (Apache-2.0), SQLite (public domain), ICU (Unicode License V3) and zlib (zlib License). The Linux checker binary links the GNU C++ library statically, under the same exception. No third-party code is sent to the browser.
The logo
An anvil drawn by Gerald G (Openclipart), from "Anvil, labelled en.svg" on Wikimedia Commons (labels by Andy Dingley, removed here; cropped). Dedicated to the public domain under CC0 1.0 Universal.