A creator code is a mechanism used in pre-Mac OS X versions of the Macintosh operating system to link a data file to the application program which created it, in a manner similar to file extensions in other operating systems. Codes are four-byte OSTypes. For example, the creator code of the HyperCard application and its associated "stacks" is WILD. This allows the application to launch and open a file whenever any of its associated files is double-clicked.

The key difference between extensions and Apple's system is that file type and file ownership bindings are kept fully distinct. This allows files to be written of the same type - TEXT say - by different applications, and freely opened by any application that can read TEXT files, but when double-clicked, will correctly open the original application that created it. With the extensions approach, this distinction is lost - all files with a .txt extension may only be mapped to a single text editing application.

Mac OS X retains creator codes, but supports extensions as well. The deprecation of creator codes (and type codes) over the older extension system, popularised by DOS and others, has been very controversial with Mac users. The type and creator system is considerably richer and more sophisticated than that provided by extensions, and many users felt that adopting DOS conventions is a backward step. They claim that type and creator information rightfully belongs to the metadata associated with a file, and is therefore illogically placed within the file's name, where its presence can cause problems for the user. Apple defend the decision by saying that extensions have become the de facto standard for indicating file type, and they need to work seamlessly with the rest of the industry.

Creator codes are not readily accessible for users to manipulate, although they can be changed with certain software tools.

See also

• type code