I want to incorporate an open source library that is GPL-3.0 licensed into my program. The library is quite big in size and I would be just fine with just a small part of it. Will removing most of its code and then using that version with my software count as modifying the original library's source code? (e.g. Will I have to distribute the source code of the library I "modified", which is basically the same with some classes removed).

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    The GPL requires you to provide source code for the version of the binary you actually distribute. I want make sure I'm reading your question correctly: is it your understanding, in asking this question, that you might be required to distribute source code that is not included in some binary that you distribute?
    – apsillers
    Commented Aug 18, 2019 at 15:43
  • The GPL also requires you to provide the source code for your whole program if you incorporate a GPL library. Don't forget that!
    – Josef
    Commented Aug 19, 2019 at 9:15
  • Even if you include the GPL library verbatim in your application, the GPL still requires that you distribute its source code. Are you trying to avoid having to provide source code available on a server? In that case you should look into providing a "written offer" instead. See section 6 of the GPL.
    – Brandin
    Commented Aug 20, 2019 at 9:04
  • @Brandin I agree with most of what you wrote, but note that per GPLv3 s6 written offers are only allowable in certain cases, none of which I think fit this one. The OP mentions nothing that suggests this is a 6b conveyance (his program binary is inside a physical object), and unless he got the GPL library inside a physical object, 6c doesn't apply either.
    – MadHatter
    Commented Aug 20, 2019 at 16:21

1 Answer 1


Per the GPL-3.0 license,

For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.

To “modify” a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission, other than the making of an exact copy. The resulting work is called a “modified version” of the earlier work or a work “based on” the earlier work.

In summary, modify is defined as anything other copying as-is; truncating a library would be considered modifying it, and therefore, requires that the adapted version be marked as such.


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