Permissive License

A permissive license is a class of open-source license that grants broad rights to use, modify, and redistribute software while imposing only minimal conditions, usually preserving the original copyright notice and disclaiming warranty. Unlike copyleft, a permissive license does not require derivative works to be released under the same terms, so a downstream developer may incorporate the code into proprietary, closed-source products.

Common permissive licenses

The best-known examples are the MIT License, the BSD 2-Clause and 3-Clause licenses, and the Apache License 2.0. The BSD 3-Clause adds a non-endorsement clause forbidding use of the author's name to promote derived products; the Apache License additionally provides an explicit patent grant. All share the core trait of letting recipients re-license freely.

Trade-offs for mining projects

Permissive licensing maximises adoption: hardware vendors and tool authors can build on the code without inheriting reciprocal source-sharing duties. The trade-off is that improvements need not flow back to the community, and a permissively licensed project can be forked into a closed product. Choosing between permissive and copyleft therefore depends on whether a project prioritises the widest possible reuse or guaranteed downstream openness.

For projects where keeping firmware auditable matters most, copyleft is often preferred; where broad ecosystem integration matters most, permissive terms win. Compare the patent and notice handling of the Apache License 2.0 for a concrete example.