We have developed a plugin based on UE4 and want to distribute it to game companies. This plugin does not modify the source code, but contains engine tools. I don’t know whether our direct distribution violates the law.
Why would you need to redistribute engine tools? You modify them? You could avoid the problem if you assume that user is required to install UE4 and used those installed tools.
No we didn’t modify the engine tools. And yes, they users can install UE4 themselves, and we just share our plugin. I wonder whether it is legal？
Since your plugin includes engine tools, you are permitted to distribute them only on the UE Marketplace.
Any public Distribution (i.e., intended for Engine Licensees generally) which includes Engine Tools (including as modified by you under the License) must take place either through the Marketplace (e.g., for distributing a Product’s modding tool or editor to end users) or through a fork of Epic’s GitHub UnrealEngine Network (e.g., for distributing source code).