This question was first posted on Open Source here.

I'll try to be more specific about what I'm doing:

After using FluentValidation for a few project I wanted to take a try at developing my own object validation API.

First I examined the code on GitHub to understand the logic that was applied. Then I went about writing my own code, it can be found here.

The API's do the exactly the same, they present very similar, they work very differently and architecturally speaking they are radically apart.

I did not copy one line of code. But I did drew inspiration from it.

FluentValidation is licensed under Apache 2.0 and at the recommendation of a user in my previous question I decided to license my project under Apache 2.0 as well, adding reference to FluentValidation's designer original copyright notice.

Apache grants "irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form."

Is it license infringement? Copyright infringement?

2 Answers 2


The "structure, sequence, and organization" of APIs are in principle copyrightable according to the Federal Circuit Court of Appeals. See Oracle v Google.

Given that the structure, sequence, and organization of an API can be protected by copyright, the analysis would proceed like this:

  • Is structure, sequence, and organization of the API sufficiently original (a product of a modicum of creativity). If yes, then the API is protected by copyright.
  • If the API is protected by copyright, then the court would apply the abstraction-filtration-comparison test to check for substantial similarity between your API and the original API.

It is possible that there are defenses to infringement or other issues that could preclude copyrightability:

  • fair use
  • merger
  • scenes a faire

As long as your software is substantially different in design (which it is) then you aren't violating copyright afaik.

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