RESW files are used by applications running under the Microsoft Windows operating system, version 8 and later. REWS files contain data that is responsible for the appearance of the user interface in terms of a specific language version. Often these files are referred to as resource files. These are text files based on the XAML markup language.

The RESW format is the successor of files with the RESX extension. In order for the RESW files to be used by the application, they are compiled into a binary result file with the PRI extension.