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I built a Qt application. Am I allowed to LICENSE it under the MIT license?

Qt is a cross-platform application and UI framework for developers using C++ or QML, a CSS & JavaScript like language. Qt Creator is the supporting Qt IDE. Qt Cloud Services provides connected application backend features to Qt applications.

Qt, Qt Quick and the supporting tools are developed as an open source project governed by an inclusive meritocratic model. Qt can be used under open source (GPL v3 and LGPL v2.1) or commercial terms.

http://qt-project.org/

Since Qt is licensed under LGPL v2.1, I guess the answer is Yes, it's fine to use the MIT license on my non-commercial app.

The LICENSING page is too complicated for me.

So, is there any problem if I licensed my app under the MIT license?

  • 2
    I'll leave answering to someone more familiar with the LGPL, but my understanding is that you may license your own code under the MIT license, and you may distribute your MIT-licensed code alongside Qt's LGPL-licensed software as a combined work. It's very important to document which components are under the MIT license and which are LGPL-licensed, so that downstream recipients (who may, e.g., want to make a closed-source project from your code) know what their right and responsibilities are for each piece of code. – apsillers Dec 29 '14 at 13:14
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No, there is no problem.

From the LGPL:

A “Combined Work” is a work produced by combining or linking an Application with the Library.

Also (emphasis added):

You may convey a Combined Work under terms of your choice that, taken together, effectively do not restrict modification of the portions of the Library contained in the Combined Work and reverse engineering for debugging such modifications, if you also do each of the following:

It then goes on to provide a short list of things you must do such as including the LGPL license with your software, display a notice in your software that it uses an LGPL library, etc. For more information, see section 4 of the LGPL license.

  • What if I change the license to GPL, should I do all these things? :-) – Ionică Bizău Dec 29 '14 at 16:32
  • That would be a different question, but the short answer is it will not change anything. – user22815 Dec 29 '14 at 16:35
  • Sure, but the short answer is it will not change anything -- do you mean that the GPL license is enough so, I don't have to add other things there (e.g. including the LGPL license)? I'm too lazy to do that. :-) – Ionică Bizău Dec 29 '14 at 16:37
  • The terms of both licenses have to be taken into account. The LGPL is specifically designed to be compatible with pretty much anything as far as linking goes (with the stipulations in my answer and the linked license text). The GPL can only be linked against open libraries: it is a little more complex than that, but the GPL and LGPL were made to be compatible on purpose. The licensing disclosures are the same as far as I remember, you still need to distribute both license texts and disclose both in your program. – user22815 Dec 29 '14 at 16:46

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