A 3DSX file is a homebrew launcher file used by 3DS software exploits such as ninjhax, ironhax, or tubehax to run homebrew. It contains executable code that is run to launch homebrew applications, which are unofficial software created by amateur developers for closed gaming systems.

On a 3DS, homebrew enables you to customize the home menu and play old SNES games and out-of-region games. The 3DSX format is designed to allow other homebrew to be launched when it is running. It also offers compatibility with future homebrew exploits as each section of the format can be independently relocated if needed. 3DSX files are not meant for use on computers as they are used on 3DS devices to run homebrew. However, you can place the 3DSX file on an SD card inserted into your Windows computer using File Explorer or Mac using Finder. The 3DSX file must be placed in the "3ds" folder in the root of an SD card in a 3DS. The 3ds folder also contains all the homebrew applications you can install to your system.