INC file is a source code development support file. INC document files store data in plain text format as as such can be viewed using any text editor. It is advised, however, that INC files be edited using professional software that offer support for development functions.

INC format can be used for various programming languages. INC files can help greatly when working with PHP and Java declarations, or with C++ functions. Many software engineers consider using INC files as bad or outdated practice and advice against it.