A CRPL file is a script saved in the Creeper Reverse Polish Language (CRPL). It contains one or more instructions that are executed to modify maps in Creeper World 3: Arc Eternal, a tower defense real-time strategy game. CRPL files may also store comments, which are preceded by #, that are added by the creator to explain the code in the file.

While CRPL files are used by Creeper World 3, they may be created and opened by any text editor since they are saved in plain text. You can add syntax highlighting and keyword auto-completion capabilities to Notepad++ by importing the crpl-syntax.xml file available on the Knuckle Cracker wiki page.