We have under development a commercial library of controls for a UI framework. An open source (MIT licenced) project wishes to use these controls and we want to let them use them.

So I guess my questions are simple:

  • Is it possible to license commercial software to a MIT-licensed project?
  • What is the best way to do this?
  • Are there any good examples of where this happens already?
  • Are you happy to have your library be redistributed under the MIT licence?
    – MadHatter
    Feb 10, 2021 at 15:00
  • No, we'd like to keep the product with a commercial license for all other customers.
    – Grokys
    Feb 11, 2021 at 7:53
  • 4
    Given that their project is currently MIT-licensed, are you confident that they want to use your library under a proprietary licence? It will make their project unusable by most free-software distribution systems, so it is at least possible that what they're asking you for is permission to reuse the library as part of their freely-licensed software. Basically, could you clarify what they mean by "they wish to use [the control library]" and what you mean by "we want to let them"?
    – MadHatter
    Feb 11, 2021 at 8:04
  • I think @madhatter asks the most important question. In what form do your customers want to use your library? Do they want to distribute it in their binaries? Feb 12, 2021 at 6:14
  • Well that's why I'm asking this question really. To give some background: one of my colleagues thinks that we can say "commercial licence, with MIT exception for X project". From my research I don't think this is possible, but I want to get a second opinion.
    – Grokys
    Feb 13, 2021 at 8:30

1 Answer 1


As we've discussed above, when you say "we want to let them use [our library of controls]", the devil is in the word use. If you're asking "can we let the members of this project run our code without having to pay for it", then the answer is of course "yes".

But I suspect that what the project wants is to incorporate your library into their project, which they distribute freely. At this point, one of two things happens: either you give them the right to redistribute your code under the MIT licence they use, in which case, your library's going to turn up in competing commercial projects quicker than you can say "AGPL"; or you allow them to use your library but only distribute it in binary form, in which case their project becomes non-free, and I suspect, non-usable.

Is it possible to license commercial software to a MIT-licensed project?

Yes, but it's not possible to license it under a weakly-free licence like MIT and retain control of your software.

What is the best way to do this?

Best is a subjective word. If it were me, I'd agree they could use my library, but only under a strong copyleft licence, such as GPLv3, or even AGPLv3. That might well mean they had to distribute their project under the same licence, a consequence that they'd have to decide whether they could endure. But it would mean that no competitor could scoop your library out of the MIT project code and lock it straight back up again.

Are there any good examples of where this happens already?

Examples, yes, but again, good is a subjective word. Examples I consider good you might consider terrible, because of the licensing implications for the formerly-proprietary code.

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