If an open source project is licensed under MIT, I want them to be able to use my library without changing their license to GPL3.

However I still want developers of proprietary applications to make their code available, since I'm going to offer a dual commercial license.


I guess one option is to offer the commercial license to open source projects for free.

  • What do you want to achieve with this license? Do you want to give maximum freedom to the end-user of a product containing your library to ensure they can always use an improved version of the library? Or do you want that others can't make money while using your library? Or something else? Aug 18, 2019 at 19:22
  • @BartvanIngenSchenau the goal is to finance the development of the library via dual licensing. So kind of like Qt's model, but with GPL so that it's not possible to use it commercially without paying. I guess one option is to offer the commercial license to open source projects for free, so that they don't have to change the license of their project.
    – Ivan
    Aug 18, 2019 at 19:31
  • I should have said "use it commercially without distributing the source code".
    – Ivan
    Aug 18, 2019 at 19:32

1 Answer 1


What you want appears basically to be source-disclosure copyleft as employed by the GPL (though you appear to tolerate nonfree terms, as long as they still include source disclosure).

In the case that an MIT projects wants to use your work, you're happy to let them do so, because they disclose their source code. But as soon as a proprietary project wants to use that MIT-licensed project (that uses your work) in a closed-source project, you don't want to allow that to happen. In order words, you want the MIT project to stop operating under permissive terms when it incorporates your work. The MIT project would have to stop being fully permissively-MIT-licensed, because after incorporating your work, it can no longer be incorporated into proprietary works without source disclosure.

In view of this fact, you may as well just use the GPL for your work, since it has virtually the same effect.

  • Thanks. So what do you think about using GPL and offer the commercial license to open source projects for free? Due to the nature of the library, it's very unlikely that another MIT project would be using the MIT project that's using the library :)
    – Ivan
    Aug 19, 2019 at 13:22

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