A library I have used has recently introduced a payment requirement, i.e buy a license code and enter it to be able to use the library. The library is however still MIT licensed. Would it be legal to fork the repo and remove the license check?

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    Based on your summary of the situation, yes, that's fine, from a copyright standpoint. It would be useful to get a link to the library in question, though, so we can check for complications (including, but not limited to, submarine patents).
    – MadHatter
    Nov 22, 2023 at 8:30
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    github.com/nager/Nager.Date this is the repo in question.
    – John
    Nov 22, 2023 at 8:39
  • Not being a programmer, I can't tell if the code in github, which is to say the code under MIT, is the entire server-side implementation, or just client-side code that contacts their server on invocation in order to retrieve the data. Hopefully, someone more versed in reading code than I can shed more light on this.
    – MadHatter
    Nov 22, 2023 at 9:27
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    @MadHatter as far as I can tell, all the data is contained in the NuGet package and there is no use of any server-side components. The license key check is also trivial; I won't post the code here but let's just say it's not cryptographically secure ;) Nov 22, 2023 at 9:39
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    @PhilipKendall that looks to me like a useful answer; care to write it up as one?
    – MadHatter
    Nov 22, 2023 at 11:17

1 Answer 1


In copyright terms, you can make any changes you like to MIT licensed software so long as you ensure that

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

That includes removing any parts of the software you don't like, including any licensing checks. Your case is very odd in that:

  • The code in question is fully client-side, it's not that the license key is used to communicate with a server-side component.
  • Looking at the code, the "license check" is trivial anyway.
  • The author presuambly knows all this.

The most likely possibility here in my opinion is that the author is using this as a very clumsy way of getting donations towards their project. That's legally fine, but I personally think they'd do better just asking for donations.

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    Also possible the idea behind this is actually get paid to provide the compiled binaries; which I do not find tacky.
    – Joshua
    Nov 23, 2023 at 2:22
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    "With a sponsorship you get the license key to use the variants locally without a dependency to our REST API" What I think is confusing things is the README is for the Public Holiday API project as a whole, not specifically for the Nager.Date code. You can use their API (which doesn't require a key, but it seems like it may in the future), or if you're using .NET you can use Nager.Date which has the data embedded.
    – Schwern
    Nov 23, 2023 at 2:32
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    I wouldn't say it's clumsy, it works rather well. To use the library, you either have to go through the hassle of forking (and maintaining that fork), or through the hassle of buying a licence key. This nudges people towards the second.
    – Bergi
    Nov 23, 2023 at 9:01
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    @Bergi when I say the license check is trivial, I really do mean it. You just need to add one line of code to your program with a simple English string. Nov 23, 2023 at 9:30
  • @PhilipKendall Oh you mean the implementation is clumsy, not the general approach. Then yeah…
    – Bergi
    Nov 23, 2023 at 9:53

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