Can your GPL software use license keys?

Back in 2007, decided to stop listing any software that used license keys. They did this because they believed that license keys were incompatible with the GPL license.

Fast forward to 2015 and many (most?) commercial WordPress plugins now use license keys. Some of these license keys just provide access to updates and support – those aren’t the issue here.

However, some license keys lock down the software to a single domain, disabling the plugin even on test sites and localhost installs.

Does this use of license keys violate the GPL?

It’s complicated.

Does using a license key to disable software violate the spirit of the GPL? Take a look at the definition of free software on the GPL site:

  • The freedom to run the program as you wish, for any purpose (freedom 0).
  • The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1).
  • The freedom to redistribute copies so you can help your neighbor (freedom 2).
  • The freedom to distribute copies of your modified versions to others (freedom 3).

If a license key disables the software in some situations, then yes – it clearly violates freedoms 0, 2 and 3. The license key impedes the freedom to run the software as you wish and redistribute the software.

However, are disabling license keys a violation of the GPL license itself? I would say no.

Read the license. I can’t see a violation. Users of software that’s blocked with license keys do get the full source code and they can edit that code to strip out the licensing restrictions. There’s nothing to stop you from distributing your software in a deliberately crippled state, but allowing experienced devs to remove those restrictions.

So, can your GPL software use license keys?

  • No, if you want to follow the spirit of the licence.
  • Yes, if you’re happy to utilize loopholes in the text of the license.

Issues like this why so many people have a love-hate relationship with the GPL.

Other thoughts on this question

Oddly, I could find very little written on this topic. I could find one blog post that addresses the questions directly:

I couldn’t find anyone explaining why they believe license keys are allowed under the GPL, althought clearly it’s possible to make that argument.

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