Game System License

The Game System License (GSL) is the alternative to the Open Game License that was created for the 4th edition of Dungeons & Dragons. It is structured to allow third-party publishers to create content for D&D, but unlike the OGL, it does not allow the reproduction of the D&D rules. The System Reference Document that accompanies the GSL is not a recapitulation of the game's rules, as was the case in 3rd Edition, but was instead an index accompanied by a number of templates to help third-party publishers reference the official rulebooks.

As the initial version of the GSL was far more stringent than the OGL, including a clause that barred third parties from selling GSL content if they were also selling OGL content (even in PDF format), many publishers initially rejected both the GSL and D&D 4e in favor of retaining their OGL catalog. The most notable of these publishers was Paizo, who revised the v3.5 d20 System into the Pathfinder Roleplaying Game in response to losing their license to publish the official D&D magazines Dragon and Dungeon.

The GSL was abandoned after the release of D&D 5th Edition, and a new OGL-compatible SRD was created for that system when the Dungeon Masters Guild program was introduced.