The question if code plugins which only dynamically link external libraries which are licensed under LGPL are allowed with Unreal Engine was already positively discussed here.
My questions is if such code plugins are allowed to be sold at the Unreal Marketplace ?
The fact, that such plugins seem to be allowed to be used with the Unreal Engine (I am only referring to the aspect of the dynamically linked external LGPL library), does not automatically mean that it is allowed to publish/sell such code plugins via the Unreal Marketplace.
Unreal EULA (B) (ii), Non-Compatible Licenses, states: “…Code or content under the following licenses, for example, are prohibited: GNU General Public License (GPL), Lesser GPL (LGPL) (unless you are merely dynamically linking a shared library)…”
Unreal Marketplace Guidelines 2.2.f, Legal, states: “2.2.f Products must not use third party software licensed under GPL, LGPL, EPL, or MSPL.”
It looks like this means that the above described code plugin (only linking dynamically an external library licensed under LGPL) would be allowed to be used with Unreal engine (because of Unreal EULA (B) (ii) ), but would not be allowed to be sold at the Unreal Marketplace (because of Marketplace Guidelines 2.2.f) ?
So, my final questions is: Would such a plugin be allowed to be sold at the Unreal Marketplace or would it be rejected because of (only) dynamically linking an external library licensed under LGPL ?
Interested in experiences from marketplace sellers & responses from Epic staff and/or Epic’s legal counsel on this subject.
P.S.: This is not about GPL, as the facts there are quite different from LGPL
Thanks for your question. You are correct that plugins that include LGPL libraries are not permitted on the Unreal Marketplace, regardless of whether the LGPL libraries are statically or dynamically linked.
I’ve got some last questions concerning this subject:
If such a plugin would be published to the Unreal Marketplace without including the LGPL library and the download of this additional library would be made available for users/buyers from another source (e.g. external website) with instructions on how to install it, would that be acceptable ?
The code plugin would not be rejected during initial checks by the marketplace team, because without downloading the LGPL library from an external source, the plugin from the Unreal Marketplace would not be functional ?
Thanks a lot for your help with these questions, I assume this subject can be helpful for other (potential) Unreal Marketplace sellers, too
It sounds like the LGPL library is necessary for the plugin to function. Simply hosting the LGPL library in a different location and asking users to download that library would still violate 2.2.f of the Marketplace Guidelines.
I summarize this to make sure that I (and potential other readers) understand everything correctly :
Code plugins using dynamically (or statically) linked LGPL libraries are not allowed to be sold/published on the Unreal Marketplace (according to Unreal Marketplace Guidelines 2.2.f). It’s not important if the LGPL library is distributed together with the plugin on the Unreal Marketplace or provided via an external source/website. The important point here is that the plugin uses a third party software licensed under LGPL and would be sold via the Unreal Marketplace.
However, if such a plugin (using a dynamically linked LGPL library) is not sold via the Unreal Marketplace but via an external Marketplace (or seller’s own website) then it is allowed to use such a plugin together with the Unreal Engine for buyers or users of the plugin (which uses a dynamically linked LGPL lib.) - according to Unreal EULA (B) (ii), Non-Compatible Licenses.
The same rules would not only apply to plugins, but also to games & applications (“products”) using both Unreal engine and a dynamically linked external library licensed under LGPL.
If I did not understand that correctly, I would be happy about a short final comment. Thanks
It is correct that while the Unreal Engine may be used with LGPL licensed libraries (provided those libraries are only dynamically linked), products on the Unreal Marketplace may not use third party software that is licensed under LGPL (regardless of whether it is dynamically or statically linked).
I am currently developing a multiplayer plugin. A UE4 code plugin without additional libraries and a server part (Java Apache Tomcat application). Both communicate via HTTP and TCP. I would like to add the Jakatar mail lib to the server app to send emails. But the lib is under EPL 2.0. Would it be possible in this case as well like with the MySQL plugin?
Yes, MIT licensed snippets/libraries are permitted in marketplace assets. You are required to declare your use of such third-party libraries using the form linked in 2.2.e of the Marketplace Guidelines (Marketplace Guidelines - Unreal Engine).