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Qt Commercial License Terms, Independent Developers

  • AFAIK, if you publish a Qt App on Play Store (or other stores) you need to keep a valid license forever. Because the license terms says you can't "distribuite" a Qt App without a license.

    This is a big problem for indipendent developers with small badgets....

  • Any news?
    It's very important to be able to use latest Qt version for non-GPL application published on stores without the need to pay a fortune.
    In particular if you don't earn anything from it but you plan to for future.

  • @luca You can still fully distribute those kind of apps under the LGPL scheme.

  • @VRonin But using Qt 5.11/QML (for example) without buying a license I suppose you must release source code.

  • @luca
    You might look at the overview in, say,

    The license allows developers and companies to use and integrate software released under the LGPL into their own (even proprietary) software without being required by the terms of a strong copyleft license to release the source code of their own components.

  • @JonB So the main difference of buying a license is that I can't statically link my App?

  • @luca
    I am not an expert, but I believe I know of three differences:

    • Yes, you cannot statically link without a license. (And I have a feeling that by definition this may exclude [certain?] mobile devices because they don't do shared libraries.)
    • I believe there are a few Qt components which are not in the Community Edition but are in the Commercial.
    • Although I pointed out above that the LGPL does not require source code publication, it does have alternative, lesser restrictions, e.g.:

    The license only requires software under the LGPL be modifiable by end users via source code availability. For proprietary software, code under the LGPL is usually used in the form of a shared library, so that there is a clear separation between the proprietary and LGPL components.

    You may avoid this requirement by purchasing a commercial license.

    Please take what I write with a pinch of salt. As I say, I am not an expert, and the advice given in this forum for this issue is to read the T&Cs carefully. I am just suggesting some avenues you may wish to investigate further.

  • @JonB So in your opinion the point of this thread (from the beginning) simply doesn't exist...
    Developing at least for Android you dynamically link to Qt so no static link (no need of license).

    For me it should be great but I'm not sure about that.

  • A requirement of LGPL is that users must be able to replace the LGPL component (Qt) with their own version so you should make sure you don't break binary compatibility (for example using the private Qt modules)

  • @luca
    Although I would not be encouraging you to not pay for Qt if you can:

    If you link dynamically to Qt, use only LGPL components, do not use private Qt modules or otherwise tinker with the Qt side, and there is nothing special about Android (I think it used to require static linking maybe, but not now) or whatever "app stores" you use, my understanding is that you do not need a commercial license.

    Basically, LGPL does not require you to publish your own source code when you link against an LGPL component, even if your app is commercial/you make money out of the LGPL usage. However, in my own case I use PyQt (Python binding to Qt), and that is GPL rather than LGPL, so I do have to make my source available if I distribute.

    All statements above according only to my understanding.

  • @JonB Thanks for the explanation.
    I would like to pay for a commercial Qt license to thanks for the good works THEY did, but at the moment it cost too much for free projects (non open source).
    The startup plan is not so expensive but it require you to pay forever if you publish your app in an app store.

    I hope Qt will find a good solution for all...

  • Moderators


    I hope Qt will find a good solution for all...

    They did, LGPL. :) You can use that with a closed source free application on a web store as long as you link dynamically and Qt can be replaced easily with a version built elsewhere.

    Since you can now link dynamically on both iOS and android you should have no issues using the LGPL license for Qt. LGPL was made for your exact use case.

    Disclaimer: IANAL make sure to check with a lawyer.

  • @ambershark said in Qt Commercial License Terms, Independent Developers:

    Since you can now link dynamically on both iOS and android

    Ah, right, is that what I was thinking I recalled when I wrote

    I think it used to require static linking maybe, but not now

    ? Have they made it so you can now but didn't used to be able to? OOI, is that a change at the Android side or the Qt side to make it possible?

  • Where can I find a list of LGPL Qt modules for a specific release of Qt ?

  • Moderators

    @JonB Pretty sure android always supported dynamic linking, although I could be wrong here, I'm not really a mobile developer. I've done one back end library on mobile and that was it.

    It was iOS that used to be static only and change to allow dynamic linking recently (like last year or 2).

  • I am an independent game author. If I use LGPL, develop a library that uses QML and dynamically links QT, and then publish it to steam, do I need to pay QT or open source?

  • Qt Champions 2019

    @Cheng-shi-hua said in Qt Commercial License Terms, Independent Developers:

    do I need to pay QT or open source?

    No, as long as you can fulfill LGPL3 you do not need commercial license and do not have to open your source code.
    LGPL3 requires you to provide users the possibility to replace Qt libraries with their own versions. This usually requires you to provide object files (.o), so users can relink. And it is not possible when using static Qt libraries!

    Keep in mind people here (me included) are not lawyers!

  • No QT official came out to clarify? This matter is important

  • Qt Champions 2019

    @Cheng-shi-hua This forum is for Qt users and not "Qt officials". If you want an answer from Qt officials then pleas ask Qt Company.

  • This is the case, thank you very much. Since it is a community, you can advertise here when I develop a game :)