I'm thinking about using the basic mechanics behind the D20 system royalty-free, however, I'm unsure if the OGL allows that. Any thoughts appreciated. And if I can't use the D20 system royalty-free, then any suggestions on other well tested systems appreciated as well.

  • Is this related to software?
    – Adam Lear
    Apr 10, 2011 at 19:21
  • Yes, I'm considering using it for a game I'm designing.
    – William
    Apr 10, 2011 at 19:25
  • @Anna: it's related to licensing, so I think it's OK... assuming he's planning to incorporate the rules in a computer game anyway. Apr 10, 2011 at 19:26
  • 1
    That's cool. Just checking that it's not a boardgame or something similarly unrelated to programming.
    – Adam Lear
    Apr 10, 2011 at 19:29

4 Answers 4


From what I understand this means the software itself does not need to be open, but the methods/data it uses that are OGL need to be available and must be the same data the program uses.

That explains that interactive games may be made using the OGL, but the d20 System is very different.

More information can be found in the Software FAQ for the d20 system.


I also am not a lawyer but I think you're heading into trouble here.

MOST of the D20 system is covered by the OGL but they deliberately omitted some critical bits so you couldn't make a complete system. There's also the issue that the OGL prohibits computer games--they are licensed separately.

  • Since you state that the OGL prohibits computer games, then this'll be the correct answer. Thanks for replying. I guess I'll look into other ideas, like Dean Harding said, maybe create my own similar system.
    – William
    Apr 11, 2011 at 7:24
  • 1
    @Loren That is wrong. The OGL does not prohibit Software at all, that is ONLY the D20 license which would not be used at all in this case.
    – Rangoric
    Sep 5, 2011 at 17:27
  • @Loren, I marked a more recent answer the correct answer, as it links directly to the FAQ concerning using D20 in software.
    – William
    Jan 9, 2012 at 22:28

I believe you are OK to do that, but I am not a lawyer. You should be able to contact the WotC and get clarification directly from them, which it what I would recommend in this particular case.

Personally, I wouldn't bother. Assuming you already know the d20 rules pretty well yourself, you shouldn't have too much trouble coming up with your own set of rules that work "like" the d20 system, but is independent of the d20 system.

Only a die-hard D&D fan would ever notice that your rules are actually different, and you completely avoid any problems you might run into with WotC.

  • Alright, I think I'll try and contact WotC first, and see what they have to say. I wouldn't mind having to add a D20 logo somewhere, as it'll serve as a proof of the underlying balance as well. I'll mark this the answer in a days time, incase someone else might know the exact answer.
    – William
    Apr 10, 2011 at 20:25

You absolutely can. You need to have all software based on the d20 SRD follow the license such as clearly marking what is and is not Open Game Content and PI.

Here is software that is actively using the OGL : http://www.dundjinni.com/eula.htm

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