At one point or another, everyone has had to change a files extension - whether it's as simple as renaming .html to .htm or something more esoteric, it's a common part of living with Windows. Depending on how you have the Windows Explorer configured this can be a fairly trivial process, but as you try to rename more and more file extensions at the same time - well, that's what this utility is all about.

Operation is straight-forward - by default it will install a shell extension, which will put it on the right click menu inside the explorer. If you have a single file selected, it will show "Rename this extension" along with the current extension in parens. With multiple files or directories, it will say "Rename these extensions" or "Rename file extensions in this directory" respectively. Selecting any of these options will launch the main application interface and automatically fill it in with the appropriate files. It is also possible to launch the application and then drag and drop one or more files onto the dialog as well.

The main window displays some helpful information about the files currently queued to be renamed, such as the full path, the filename, the current extension and the filesize. Any column can be clicked on to cause it to be sorted, and clicked again to have it sort in the opposite direction. A context menu is also available when you right-click on any of the files in the main dialog, from here you can perform some helpful operations on the list:

    Remove:         As the name implies, this removes any selected files from the list.
    Open Folder:    This opens the folder that the selected file is in.
    Lookup Online:  This launches the web browser and opens the specific
                    page on a website that tracks information about each
                    file extension, what programs use it, etc.
    Lookup Google:  This launched the web browser and searches Google
                    for references to the particular extension.
    Test Extension: This allows you to quickly see what will happen if you
                    rename the file to another extension.  It takes the
                    current extension specified on the main dialog, copies
                    the file into a temp directory, renames it, and then
                    attempts to launch the application now associated with
                    it.
    Properties:     Opens the file properties dialog.

To rename the files, make sure only the files you're interested in are in the list, then specify the extension you want to rename them to, and finally click the 'Rename' button, sit back and wait - that's it. The actual rename progress is tracked and updated as it goes, in general it can rename several thousand files in just a couple of seconds.

On the configuration dialog you can tweak some of the more advanced features of the application. If you don't want to have it show up in the Windows Explorer (or other shells), then uncheck 'Integrate with Explorer right- click'. By default if it is unable to rename a file, it will stop the process, leaving any files it hasn't renamed yet in the dialog. If you would like it to continue (but still leave the offending files in the dialog), uncheck 'Abort on failure'. If you tend to just launch the app to rename something and then exit, then 'Exit when done' is a great feature to save you having to close it. 'Disable type icons in list' simply removes the icons from the main file list - this speeds things up a bit, but probably only makes any real difference on slow machines. With 'Process sub-directories' turned on, when a folder is passed into the program it will include any files inside of it or also inside of folder inside of it. Extension case will automatically lock the case of the extension to either upper or lower case, or mixed - it's worth noting that this has now impact on how the extension is processed, it's purely a cosmetic decision.

Logging is one of the more critical aspects of the program - by default it will log everything it renames, and in general this is a really good idea to leave enabled. The logs are necessary to allow the application to 'undo' any renames that you do in case it was a mistake or something else comes up. In order to undo, just click on the 'Undo' tab in the config and then click the 'Undo' button. The log files themselves are in plain text and can be viewed using Notepad to verify they are what you think they are and that you're undoing the correct batch.

Special thanks goes out to Marco at Snapfiles.com, who recommend it as well as helped test it.