Filename Extensions

A filename extension is a set of characters added to the end of a file name that determine which program should open it. A filename extensions indicates the type of information stored in the file. For example, in the filename EXAMPLE.TXT, the extension is TXT, which indicates that the file is a text file.

For example:

• xlsx means that a file is an Excel spreadsheet file,
• rar means that a file is a WinRAR compressed archive,
• htm is a HTML document,

and so on.

In Windows, if the extension is associated with an application, then you can just double-click on the file's icon to open it.

Windows normally hides filename extensions

Follow these steps to choose whether Windows displays these file extensions.

• Open Folder Options by clicking the Start button, clicking Control Panel, clicking Appearance and Personalization, and then clicking Folder Options.
• Click the View tab, and clear the Hide extensions for known file types check box, and then click OK.

More information about file extensions is available on Wikipedia.

Directions for use

• To search for filename extension, type it into the search field at the top of this page, and click on the "Find" button. For example, to find information about the .xlsx extension, simply enter xlsx into the search field at the top and click on the button.
• Only exact extensions must be entered for a search, the wildcard characters (like "*", "?", etc.) are not allowed!
• If you can't find an extension here, please come back later, our extension database is updated daily!

If you know about an extension

If you find a new extension, a related link or useful information about extensions, then please click on the "Submit New" button at the top of page and contact us.