copyleftincompatible

Copyleftincompatible is a term used in open source and free software licensing to describe licenses whose terms cannot be reconciled with the terms of a copyleft license, such as the GNU General Public License (GPL), when used in the same software project. A license is considered copyleftincompatible if a derivative work that combines code under that license with code under a copyleft license cannot be distributed under the copyleft license without violating one or both licenses.

Compatibility is typically evaluated on a license-version basis and arises from terms that conflict with the copyleft mechanism. Common sources of conflict include additional restrictions beyond the copyleft requirements (such as advertising or use restrictions), conflicting patent terms, or clauses that limit redistribution in ways incompatible with the copyleft license. If a combined work cannot be redistributed under the copyleft license, developers must either separate the components, obtain an license exception, or choose a different license that is compatible with the copyleft license.

Examples frequently cited as copyleftincompatible with major copyleft licenses include certain permissive licenses with extra restrictions and some non-permissive licenses that impose terms conflicting with copyleft needs. Notable discussions of compatibility are maintained by organizations such as the Free Software Foundation, and compatibility status can vary by license version. When composing a project, practitioners are advised to consult compatibility resources and consider licensing choices carefully to ensure lawful distribution of the combined work. See also copyleft, GPL compatibility, license compatibility.