The Half-Life SDK is a collection of applications used for developing maps and modifications for games that use Valve's GoldSrc engine. Along with the packaged programs, the SDK also includes model sources and source code for the engine and various entities used within the games.
The Half-Life SDK contains many programs useful for editing GoldSrc-based games, such as Half-Life. It also contains the source code for Half-Life, Deathmatch Classic and Ricochet, which can be edited to introduce new entities, monsters or left as is and used as a base. It also contains 3DS Max and .smd source files for models, and sources of two Half-Life storyline maps and one map used as beam demonstration.
The Standard SDK contains source code, launcher graphics toolkit and several help files along with all content from Model and Map SDK, Texture SDK and Sprite SDK.
The Full SDK contains everything that Standard SDK includes and also sources for certain monster models and all weapon models. Before SDK version 2.1 it was given only to modders who have signed a non-disclosure agreement with Valve and was known as Professional SDK.
Source code only
A special edition of SDK, containing only source code, exists for version 2.3, which does not exist in Standard edition.
Model and Map SDK
The Model and Map SDK, commonly known as Mini SDK, contains player model sources, sources for Gluon Gun and MP5 models, Valve Hammer Editor, sources for two storyline maps and one beam system demonstration map and networking code help file. Its content is included in Standard and Full editions.
The Texture SDK contains only parts necessary for texture creation. Its content is included in Standard and Full editions.
The Sprite SDK contains only parts necessary for sprite creation. Its content is included in Standard and Full editions.