License identifiers

The accepted set of values for metadata.license and spec.skills[].license. Both fields share the same enum, so the same identifier means the same thing whether it's applied to the agent as a whole or to an individual skill.

Accepted values

Identifier	Notes
MIT	Permissive
Apache-2.0	Permissive, patent grant
BSD-2-Clause	Permissive
BSD-3-Clause	Permissive
GPL-2.0	Copyleft
GPL-3.0	Copyleft
LGPL-2.1	Weak copyleft
LGPL-3.0	Weak copyleft
MPL-2.0	Weak copyleft
ISC	Permissive
CC0-1.0	Public domain dedication
CC-BY-4.0	Creative Commons, attribution
CC-BY-SA-4.0	Creative Commons, attribution + share-alike
Unlicense	Public domain dedication
Proprietary	Closed-source / all rights reserved

Rules of the road

• One identifier, not an expression. SPDX expressions such as MIT OR Apache-2.0 are not currently accepted; a single identifier only.
• Mirrored in skill frontmatter. For skills, the license value mirrors the license field in the skill's SKILL.md frontmatter so the licence travels with the playbook regardless of where it's consumed.
• LICENSE file is optional. Shipping a separate LICENSE file alongside SKILL.md is not enforced by the schema - consumers MAY include one in the skill's source directory if their distribution channel expects it.
• Additive growth. New identifiers may be added in future minor versions of the schema; existing manifests stay valid.