Inside the patch
What is an xDelta file?
An .xdelta file is a patch: data and instructions for rebuilding a changed file, usually from a specific original.
How an xDelta patch works
The patcher reads the original file and follows the patch’s instructions to create a new output. These instructions can copy existing data, add new bytes or repeat data. Unchanged parts can be reused without including another full copy of them in the patch.
xdelta3 uses the VCDIFF differencing format. The format works with binary data; it is not specific to one console or filename extension. A patch may be small compared with the output, but its size depends on how much the data changed and how the patch was encoded.
Why creators distribute patches
ROM hacks, translations and other file modifications can be distributed as patches so users can apply the changes to their own matching originals. This site provides the patching tool, not game files or patch downloads. Use only files you are permitted to use.
A patch is not necessarily free of material from the target file. It can contain newly added bytes as well as instructions that reuse source data. Its filename alone says nothing about permission to distribute its contents.
Why the original must match
A patch created for one revision may read the wrong data from another. Region differences, earlier modifications, headers or trimming can change the bytes it needs. The patch creator’s required source takes priority over a file’s name.
When a patch includes output window checksums, xdelta can detect mismatched reconstructed data. If this fails, see how to troubleshoot a checksum mismatch. Not every patch contains checksums, and a successful decode is not a guarantee that a game will work in an emulator.
Open and apply an .xdelta file
An .xdelta patch is not the finished game or file. Apply it to the required original using xDelta Patcher online. Select your original, select the patch, check the output name and apply it. A separate output is then offered for download.
If your patch is inside a ZIP, this tool can extract the .xdelta entry. Other patch formats require a patcher that supports them. Renaming a file’s extension does not convert the patch.
Follow the complete step-by-step guide →
Further reading
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