Diamond is released under GPL version 2. The following is the license which will appear in all source files for Diamond.

    Copyright (c) 2012-2021 Barbara Geller

    Diamond Editor is free software: you can redistribute it and/or
    modify it under the terms of the GNU General Public License version 2
    as published by the Free Software Foundation.

    Diamond Editor is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    General Public License for more details.