.XNB File Extension
File TypeXNA Game Studio Binary Package
This file is saved in a binary format, which requires a specific program to read its contents.
Binary data file created with XNA Game Studio Express, an IDE designed for developing Windows and Xbox 360 games; contains one or more files in a single package.
The XNB format is considered an "intermediate format" since it packages original files into an proprietary file type. XNB files are referenced by games created with XNA Game Studio Express and are not meant to be opened manually.
An example game that uses XNB files is Terraria, a 2D action and adventure game. Terraria stores graphics, audio, and other game data using XNB files.
NOTE: While most XNB files cannot be opened directly, image files, such as .PNG images, may be extracted from an XNB file using a program like GXView (part of The GameTools Suite).