System Reference Document

The System Reference Document, or SRD, is a set of reference role playing game mechanics licensed under the Open Game License by Wizards of the Coast (or WotC) and based upon their Dungeons and Dragons role-playing game. The SRD forms the basis of WotC's various d20 System role-playing games, including the d20 System itself, d20 Modern and d20 Future. The SRD is also the basis for role-playing games published by companies other than WotC; these include Mutants & Masterminds, Arcana Evolved, Labyrinth Lord, and OSRIC, among others. Some other game systems (such as FATE) have also released their own mechanics under OGL-licensed "System Reference Documents" of their own; however, this article discusses specifically the d20 System SRD.

Formats
The SRD is freely available from the WotC website as a series of Rich Text Format documents. It is also available from a variety of other sources which provide alternate formats and/or additional OGL material (see References).

A 4th Edition SRD is available as well.

Scope
The SRD specifies the skeleton rules and mechanics&mdash;including races, classes, feats, skills, spells, magic items and monsters&mdash;compatible with the d20 System version of Dungeons & Dragons editions 3.0 - 3.5 (the 4th edition represents a substantial revision) and various other roleplaying games from Wizards of the Coast. It is continually updated to comply with errata issued by WotC. Compared to the published source books for the Dungeons and Dragons game, the SRD provides the same basic rules but lacks "flavour" elements. There are no named gods, none of the spells have significant NPC names, there's no mention of Greyhawk or other copyrighted works by WotC. There are also no rules for character creation, for advancing characters in level, calculating experience, or anything else related to the topics forbidden by the d20 System License. Certain monsters - most notably Illithids (Mind Flayers) and Beholders - were also left out of the SRD.

Absence of Greyhawk references
As mentioned above, a spell such as "Mordenkainen's Sword" becomes "Mage's Sword" in the SRD due to the omission of D&D's default setting which is a simplified version of the Greyhawk campaign setting. Greyhawk's rich history also provides many of the magic items, artifacts and flavour of the core rules, and each of those have either been left out of the SRD or changed to more generic names. This was done as the proper names of the items are the intellectual property of Wizards of the Coast. If they had been published within the SRD (or later the RSRD for D&D3.5), then they would have become part of the Open Gaming Content that any company could use, subject to the terms of the Open Gaming License.

Overview of the system
The SRD presents a class-based game system, which is to say that it presents a set of mechanics for describing archetypical characters. A player may select such fantasy standards as the "fighter" or "wizard" and then customize their character as needed. It also presents a level-based game system, which is to say that characters progress by increasing their archetypical class's "level", gaining new abilities as they do so.

Characters are further customized with skills (such as "climb" and "diplomacy") and feats (such as "two-weapon fighting" and "diehard"). Certain classes also gain the ability to manipulate magical spells or psionic (mental) powers.

The referee (called a "dungeon master") is presented with mechanics for resolving character actions and combat, as well as a large list of "monsters" (which generally means any creature, sapient or otherwise, which is of a race other than those available to player characters, although, creatures of these 'civilized' races often make the most formidable and challenging 'monsters') and treasures with which to reward the players.

Genre
While the SRD presents a distinctly fantasy-themed set of rules, the mechanics which it outlines were designed to be adaptable to nearly any genre. However, there are limitations. Because of the focus on classes, adapting the system to highly variable settings such as a superhero game is difficult (e.g. Mutants & Masterminds).

4th Edition System Reference Document
The 4th edition System Reference Document presents a system much like the one just described, however, the manner of presentation is quite different. Whereas the 3.5E SRD presents complete information about races, classes, combat formula, spell effects, and so on, the 4E SRD presents only lists of concepts and tables from the 4E Player's Handbook. One can not read the 4E SRD by itself and understand thereby how to design a game. Instead, one must look up the parts of the Player's Handbook that are referenced in the SRD, and construct a game system from those elements of the Handbook.