Can I legally register a file extension?

There is no "official" file extensions database, so it is not possible to legally register a file extension and prevent others from using it. Because of this, many file extensions have more than one file association.

In 2009, became the central file extensions registry, recognized by Microsoft as the authoritative source of file extensions and associated file types. Therefore, if you are a software developer, the best way to reserve a file extension is to submit it to

Submit a File Type

If you are developing a software program and have one or more file extensions you would like to use, you can submit the extension(s) to Before submitting an extension, we recommend that you first search for the extension. If the file extension is already associated with another program, it is best to choose a different one.

NOTE: Even if a file extension you would like to use is not found in the database, you may want to search the web for the extension to make absolutely sure it is not being used by another program.

Once you have found a unique file extension you would like to use with your program, you may register it with Make sure you include a detailed description of both the file type and the program that will use it. After verifying the information, our team will add the extension to our database, and it will appear on