I have bit similar question to Optionally Using GPL Library via System API in Closed-Source Application but not 100% the same.

Let's say I have closed application A (i.e. frontend application). It is exposing API keeping rights to it, but grants open rights to execute it (code is closed, API is publicly available).

Then is app B (i.e. backend admin panel) which is GPL admin for GPL C (i.e. frontend application). If I fork B and add support for A API and publish back under GPL is it still ok?


  • 3
    You need to add some details to make your question understandable. What does "GPL admin for" mean? For example, what kind of software is "GPL C" and how exactly it is related to B?
    – Doc Brown
    Commented Nov 21, 2016 at 11:05
  • @DocBrown added explanation. As admin I meant admin panel / management / backend part of the app. Both A and C are frontend apps (being managed by B) Commented Nov 21, 2016 at 12:14

1 Answer 1


Lets say A is an application like "Microsoft Office", and C is "Libre Office". Now you can write (or extend) a GPL application B which uses the APIs of Word and Libre Office to allow some administrative work for both applications. As long as you publish your modifications to B under GPL again, IMHO that is fine.

It could be quite different if Microsoft would take your open source application B, integrate it into Office without asking you for a permission or different license, and then try to redistribute the new combination. Note this is an artificial, hypothetical scenario, which I don't expect to happen in reality (at least not specificially with you and Microsoft as actors ;-) ).

  • Actually its first great. To make it clearer I wanted to build kind of frontend that could be controlled by Wordpress Calypso. If I publish my improvements to Calypso under GPL I understand it should be still fine as it will consume API of my product, not another way around. Thank you. Commented Nov 21, 2016 at 12:35

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