A GD file contains source code written in GDScript, which is a scripting language used to create and modify content in Godot Engine. It stores code in a syntax similar to Python, which may include identifiers, keywords, operators, variables, constants, functions, and comments. GD files may be executed in Godot Engine or edited with Godot Engine or a text editor.

Godot Engine is an open source game engine used to create 2D and 3D games for Windows, macOS, Linux, Android, iOS, and the web. GDScript was created by the Godot community to provide custom integrated features that other programming languages, such as Lua, Python, and Squirrel did not provide out-of-the-box. GD files may be run in Godot Engine or they may be edited with the script editor that comes with Godot Engine. The script editor includes helpful editing features, such as code completion and syntax highlighting. Developers may also edit GD files with plain text editors, such as Microsoft Notepad and Apple TextEdit, but they do not provide the same scripting features as Godot Engine. NOTE: GDScript was introduced with version 3.1 and later of Godot Engine.