What is .FGD file extension?
Game definition file used by Hammer Editor, a component of the Source SDK used to make map files for Valve games; describes all entities used by a game; enables game modifiers to reference game entities when creating custom game modifications.
FGD files are available for popular Valve games, such as Half-Life, Counter-Strike, and Team Fortress Classic.
NOTE: The Hammer Editor program was originally developed using the name "The Forge," which was used as the basis for naming FGD files.
You can see a list of software programs here on www.easyfileopener.org that can open this file type so that you don’t need to search for it on the web. You can then open your file with this extension using a software listed below.