Glossary of Computer File Extensions

Filename Extensions List

So you see a file somewhere on the 'net with a name like "" and you would like to download it and use it on your computer. Will it work? What does the file extension xyz mean, anyway? This handy guide attempts to provide answers to those questions.

It is not meant to be read straight through; rather, it is meant to be a reference. An extension may be looked up either with the "find in page" option of your browser or by appending a "#xyz" (without the quotes and with xyz replaced by the extension in question) to the "go to" or "URL" field on your browser. There is also a Search Interface that will return not only the specific extension sought but also other entries that reference it. Be aware though that it assumes familiarity with the computer basics discussed on the terms page.

You may notice that most extensions are three letters (or fewer) long. This is due to a historical limitation of the operating system called CP/M (that was later inherited by MS-DOS). In fact, the whole concept of file extensions comes from CP/M. Most modern operating systems do not attribute any special meaning to the "." (period, or dot) character.

Be aware though that there is no standardization to filename extension usage, and many different people have used extensions to apply to many different things. This list only attempts to provide likely guesses of what something is apt to be. Programs that can make use of many of these extensions can be found on the Guide to Free Software.

If you want something added or see a problem with something already here (but keep in mind this guide is not meant to be overly technical) please send .

A file with this extension normally contains calendar information. It should be in simple ASCII and should be usable on any machine with software that supports the iCalendar standard.
The image file format was originally created for the Amiga but can now be read by numerous different image manipulation programs for several different platforms.
This indicates an Adobe InDesign native format document. Such a file may only be read with InDesign (currently only available for a price on Mac & WinTel platforms).
This indicates an Adobe InDesign native format template. Such a file may only be read with InDesign (currently only available for a price on Mac & WinTel platforms).
A source file written in the Inform language (a language optimized for creating interactive fiction). Inform compilers have been ported to virtually every platform in use today, and will create either Z-machine code or Glulx code depending upon the specifics of the compiler.