What Is a DIFF File?

How to open, edit, and convert DIFF files

A file with the DIFF file extension is a Difference file that records all the ways that two text files are different. They're sometimes called Patch files and use the .PATCH file extension.

A DIFF file is normally used by software developers who are updating multiple versions of the same source code. Since it explains how the two versions are different, the program that uses the file can understand how the other files should be updated to reflect the new changes. Performing this type of modification to one or more files is called patching the files.

Some patches can be applied to files even if both versions have been changed. These are called context diffs, unified diffs, or unidiffs. Patches in this context are related, but not the same, as software patches.

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DIFF files, which this article is about, are not the same as DIF files (with only one F), which might be Data Interchange Format files, MAME CHD Diff files, Digital Interface Format files, or Torque Game Engine Model files.

How to Open a DIFF File

DIFF files can be opened on Windows, Linux, and macOS with Mercurial. The Mercurial Wiki page has all the documentation you need to learn how to use it. Other programs that support this format include GnuWin and UnxUtils.

Adobe Dreamweaver can also open DIFF files, but we assume that would only be useful if you want to see the information that's contained within it (if possible), not for actually using the file like you can with Mercurial. If that's all you need to do, a simple free text editor works, too.

If all else fails and you still can't get your DIFF file to open, it may be completely unrelated with Difference/Patch files and instead used by some other program. Use a free text editor, or the HxD hex editor, for help finding out what program was used to create that specific file. If there's anything useful "behind the curtain," so to speak, it'll probably be in the header portion of the file.

If one program on your computer tries to open the DIFF file but you'd rather a different installed program do it, you can change which program opens the file by default.

How to Convert a DIFF File

Most file types can be run through a file converter tool to be saved in a new format, but there's no reason to do that with a DIFF file.

If your file happens to be unrelated to the Difference file format, then the program that opens your specific file might support exporting or saving it to a new format. If so, that option is probably somewhere in the File menu.

Still Can't Open the File?

Some file formats use a similar extension—DIX, DIZ, and PAT are a few examples—but they aren't the same thing. If your file isn't opening using any of the programs mentioned above, you might want to check that you're reading the extension correctly.