Suppose I was selling a "mod" of an app. You'd purchase the mod, download it (app not included), and run its installer to inject it into the desktop app, so that every future launch of the app would include the mod. The mod would contain only my code, and no one else's. Would this be legal? I am an American. The app in question is a popular electron desktop app.

  • 1
    Does this answer your question? Can someone claim copyright infringement after-the-fact? Commented Dec 9, 2022 at 15:02
  • Sort of. It asks about whether the original app is copyrighted, but there's no clear explanation of how a mod would fall under an app's copyright. AFAICT, there is no copyright violation for this hypothetical mod since I'm only selling my own intellectual property, but maybe I'm wrong.
    – hodler
    Commented Dec 9, 2022 at 15:20
  • My intuition is that the correct answer would be more clear if the context and nature of the mod were spelled out more. The issue is derivative work liability and that tends to be highly context specific.
    – ohwilleke
    Commented Dec 9, 2022 at 17:58

2 Answers 2


The purpose of this "mod" appears to be to create an unauthorized derivative work of the original copyrighted app. Running the mod and thereby creating such a derivative work would be copyright infringement unless fair use or another exception to copyright applies, and there is not enough info inn the question to come to any conclusion on that point.

Creating the mod itself would seem not to be infringement. However, distributing it with the intention that others, running it, will create such a modified version of the original app might well be contributory infringement. There are signifgicant possible problems here that the answer by user6726 does not address.

  • Thanks. It still seems odd, because the mod is what I'm selling, not the derivative work that can be created with it
    – hodler
    Commented Dec 9, 2022 at 18:37
  • @hodler Yes, but your business model works because you are selling to people who you have good reason to believe will use it to violate the law. It is a little like selling glass cutters in a drug marketplace--you would know that people are often buying them to commit break-ins. Not quite the same thing, but it may help one see the point. Or it is like one who sells access to a site that hoists pirated works. Commented Dec 9, 2022 at 19:08
  • What about the many popular chrome extensions that modify all web sites by default? Vimium and dark reader being two examples
    – hodler
    Commented Dec 18, 2022 at 18:53
  • @hodler those do not modify the sites in place, to the best of my understanding.. Rather they modify how the browser displays them. Commented Dec 18, 2022 at 18:58
  • There is no distinction between the “site” and how it is displayed. The navigation and design of a site are specified in code just like everything else, and these extensions modify them. And things like the design are also under copyright, no? And there are many examples of extensions that are even more intrusive, such as Grammarly
    – hodler
    Commented Dec 18, 2022 at 21:04

Since what you are distributing is (by your stipulation) entirely your own creation, you can sell it or give it away as you like. You can't include portions of the host program without permission of the copyright owner. I also don't address the possibility that you are contractually prohibited from doing this (creating you program requires use of software licensed under the condition that you not use it to engineer add-ons etc). This is analogous to writing a Word macro, which takes advantage of the fact that Word can execute programs.

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