How to Open an IDX File Extension

By Isobel Phillips

The IDX extension is a generic extension for index files. Index files are created by the search function of an application in order to make searches more efficient. There are at least 19 software programs that create index files with this extension so there isn't a single application that opens all of them. IDX files can be large and you may be able to delete them if you can establish that they're not critical to the operation of a program.

Things You'll Need

  • Windows Explorer

Step 1

Open Windows Explorer by clicking on "Start" and then "Computer." In the menu bar, click on "Tools" and "Folder Options" and click on the "View" tab. Check the radio button next to "Show hidden files and folders" and uncheck the box next to "Hide extensions for known file types." Click "OK" to save your settings.

Step 2

Navigate to the folder that holds your IDX file. Click on the down arrow next to "Views" in the Toolbar and select "Details." Hold your cursor over the title bar of the "Name" field, right click and choose "Size Column to Fit." This will show the full name of every file, including the extension.

Step 3

Right click on the title bar of the "Name" field again and choose "Type." If you can't see "Type" in the options available, click on "More..." at the bottom of the tab, scroll down the list that appears and check the box next to "Type" and then click "OK."

Step 4

Click on "Type" in the title bar of your folder to sort the files by type. You can often work out which type of IDX file you have by looking at the other files in the same folder.

Step 5

Open IDX files with SUB files using DVD playback software. If you see files with a .SUB extension in the same folder as your IDX file, your IDX file is almost certainly a subtitle file for a DVD and should not be deleted. It will open automatically when the DVD is played. VideoLAN VLC Media Player opens this file on all operating systems.

Step 6

Open IDX files with MBX files using Outlook Express. Files with the extension .MBX in the same folder as your IDX file are Outlook Express mail messages. You will need the IDX file to import old Outlook Express mailboxes from Version 4 or earlier into later versions of Outlook Express.

Step 7

Open all other IDX files using the associated application. In any other case, your IDX file is almost certainly a general index file. You can often delete this type of IDX file and the application will create it again as necessary, but you cannot open it in any other software.

Tips & Warnings

  • If you get an error message that an application "Cannot open IDX files," uninstalling and reinstalling the software will usually prompt the software to create a new index.
  • Large numbers of IDX files that appear in My Documents after copying a CD can be safely deleted once the copy has been verified.
  • Deleting Outlook Express IDX files will also delete all the associated messages.