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Qt License Inquiries



  • Dear All,

    I am currently evaluating Qt (I am new) for a new client's project. The client is an organization, and the application is used for safety and security.

    Project Overview:

    • The project's back-end is written in Python and running on a dedicated server.
    • The project's desktop client is running on a Windows 10-based workstation. This is where I wanted to use Qt. The desktop app will talk to the backend server via an API we develop using Flask. I haven't decided yet whether to use Qt (C++) or PySide (Python).
    • The project's mobile client is running on an iOS-based tablet which is written in Python/Kivy and talks to the backend server through the same API.

    I've been checking Qt for a few weeks now, but haven't read the licensing thoroughly not until now though. From what I read, Qt is available in 3 licenses: GPLv3, LGPLv3, and Commercial. Commercial licensing is out of the picture at this time. GPLv3 is not acceptable at this time as well due to some undisclosed restrictions on my side. So my only choice is the LGPLv3 (at least at the moment) as LGPLv3 allowed distribution without releasing the core source code of the app to the client. We can oblige to the LGPLv3 requirement by providing a license page, a Qt source code downloads link, etc. on the client application.

    I checked the Qt Feature page (https://www.qt.io/product/features) to identify which are the things we can use under LGPLv3:

    Under SDLC Core Activity, I chose "Develop"
    Under Qt Packages, I chose "Qt for Application Development"
    Under License Models, I chose "LGPL v3"
    Under Development Platforms, I chose "Windows"
    Under Target Platforms, I chose "Windows" ---- and this is where the issue comes (not sure whether this is an issue or what). Whenever I chose the target platforms to Windows, the Licence Model is going back to "Commercial". I did try changing it back to "LGPL v3" but the Target Platform is changing to "Linux/X11".

    Please pardon me for some silly questions:
    Q1. Does this mean I am not allowed to use Qt if my target deployment is Windows?

    I will wait for a kind soul to answer my silly question.

    Kind regards,
    Braynex


  • Moderators

    You definitely can use Qt LGPL on Windows.



  • @sierdzio said in Qt License Inquiries:

    You definitely can use Qt LGPL on Windows.

    Dear sierdzio, thank you so much for the response, I appreciate it very much.

    Kind regards,
    Braynex



  • @sierdzio said in Qt License Inquiries:

    You definitely can use Qt LGPL on Windows.

    Hi sierdzio, sorry for the follow-up question. I updated my post above before I read your reply.

    My follow-up question is whether Qt LGPL is ok for B2B as well?
    I asked because the desktop client is used for safety and security monitoring by an organization (the client).

    Kind regards,

    Braynex


  • Moderators

    @Braynex said in Qt License Inquiries:

    My follow-up question is whether Qt LGPL is ok for B2B as well?

    The LGPL license does not place restrictions on what the software can be used for. So yes, you can use LGPL'ed software for a B2B project.

    this is where the issue comes (not sure whether this is an issue or what). Whenever I chose the target platforms to Windows, the Licence Model is going back to "Commercial". I did try changing it back to "LGPL v3" but the Target Platform is changing to "Linux/X11".

    This looks like a bug in the Qt website: https://forum.qt.io/topic/123280/qt-features-page-working-correctly



  • @JKSH said in Qt License Inquiries:

    @Braynex said in Qt License Inquiries:

    My follow-up question is whether Qt LGPL is ok for B2B as well?

    The LGPL license does not place restrictions on what the software can be used for. So yes, you can use LGPL'ed software for a B2B project.

    this is where the issue comes (not sure whether this is an issue or what). Whenever I chose the target platforms to Windows, the Licence Model is going back to "Commercial". I did try changing it back to "LGPL v3" but the Target Platform is changing to "Linux/X11".

    This looks like a bug in the Qt website: https://forum.qt.io/topic/123280/qt-features-page-working-correctly

    Dear JKSH,

    Thank you for responding to my inquiries, I appreciate it very much.

    I see that the guy who started the other thread experienced the same issue (bug) on the Features page, thank you for the clarification. I really thought that we can't target Windows-based Platforms and almost gave up lol.

    Based on the response from you guys, we are now ready to adopt Qt for our next project.

    Kind regards,
    Braynex



  • @Braynex said in Qt License Inquiries:

    I haven't decided yet whether to use Qt (C++) or PySide (Python).

    Just to remind you of one thing. If you choose Python you must adopt the PySide you mention, either PySide2 or the new PySide6. Don't be tempted to pick the better known/more-featured PyQt5 or PyQt6 you will see around the web, because that requires GPL rather than LGPL. No such issue if you go C++.



  • @JonB said in Qt License Inquiries:

    @Braynex said in Qt License Inquiries:

    I haven't decided yet whether to use Qt (C++) or PySide (Python).

    Just to remind you of one thing. If you choose Python you must adopt the PySide you mention, either PySide2 or the new PySide6. Don't be tempted to pick the better known/more-featured PyQt5 or PyQt6 you will see around the web, because that requires GPL rather than LGPL. No such issue if you go C++.

    Hi JonB, noted, thank you for the tips.

    Our first choice is PySide6 for this project because PyQt's GPL licensing is out of the picture due to the nature of this project.

    Kind regards,
    Braynex