So I am doing a side project to build a platform where different groups of people can play D&D 5e online. While looking for resources online, I stumbled across the OGL. Now the OGL has a lot of data but doesn't have the complete data (for eg, class archetypes are not present). Now I want to know if there is any way how I can use the data not falling under Open Game Content.
Sure there is—pay Wizards of the Coast to license that material.
The Open Game License is free, but only covers a subset of the game. Often it covers just one example of each kind of thing. In order to include the rest of the content, you need to license it from Wizards of the Coast—but they don’t offer it under the Open Game License, so you’ll have to get it under some other license, which won’t be free.
This is precisely what, for examples, Fantasy Grounds and Roll20 have done. They pay Wizards of the Coast some amount of money, and receive a license to include 5e content beyond what’s available under the OGL on their platforms. How much they pay, the exact terms of this license, are not public information. Wizards of the Coast does not simply have a store somewhere selling licenses of its content. Instead, those licenses and the associated licensing fees are negotiated between Wizards of the Coast and whoever is doing the licensing.
Notably, both Fantasy Grounds and Roll20 were existing, functioning platforms before 5e even existed. Part of the “payment” that Wizards of the Coast might demand may be some kind of assurance that your platform is going to be a real thing that people really use, because part of the value they derive from selling these licenses is the increased exposure of D&D via these platforms. So if you’re still working on the platform, they may not be interested in even negotiating a payment. Or maybe they are—again, these aren’t public details, so there’s no way for us to really know. There is presumably some amount of money you could throw at them to get them willing to pay attention even if they have doubts about your platform.
Here is the guide to the use of Wizards of the Coast intellectual property:
Two parts that are most interesting to you are:
Can I use all of Wizards’ IP?
Unfortunately, no. You cannot incorporate Wizards patents, game mechanics (unless your Fan Content is created under the D&D Open Game License), logos, or trademarks into your Fan Content without our prior written permission.
If your Fan Content isn’t covered by this Policy, you’ll need our prior, written approval. If you have any questions or the Fan Content you want to make isn’t covered by this Policy, contact us by logging into the Wizards Help System at https://support.wizards.com. We’ll reply back as soon as we can.
Please understand that if you don’t hear from us, it does not mean we approve of your requested use of Wizards IP; it probably just means your question is covered by the Fan Content Policy.
So, by their FAQ, if your creation does not fall under OGL, you are supposed to log in to their support system, and ask.