PatchMyROM

xdelta Patcher

xdelta handles the ROMs other formats weren't built for — mainly large Nintendo DS games. It runs here the same way everything else does: locally, in your browser.

XDelta

Great for large ROMs

A Tool Borrowed From Outside ROM Hacking

Unlike IPS, UPS, or BPS, xdelta wasn't built for ROMs at all — it's a general binary diff format used well beyond gaming. The ROM hacking community picked it up because it scales to much bigger files without the diff itself becoming unreasonably large. That's exactly the situation Nintendo DS ROMs create: they're an order of magnitude bigger than the GBA and SNES games most other patch formats were designed around.

Step-by-Step

1

Have your base ROM ready

xdelta patches for something like an NDS game can mean waiting on a file that's tens or hundreds of megabytes — make sure you've got it before you start.

2

Get the .xdelta patch file

These are usually distributed as a single file. Double check it's meant for your exact ROM revision.

3

Load both files into the patcher

Large files take a moment to read — the tool shows real progress while it works through them.

4

Download the result

The patched ROM is assembled locally and offered as a normal download once it's done.

Patch an xdelta file now

Mistakes That Trip Up xdelta Patching

Expecting xdelta to be ROM-hacking-specific

It isn't — xdelta is a general binary diff tool the ROM hacking community adopted because it handles large files well. That also means it doesn't carry ROM-specific conventions the way IPS or BPS do.

Using a differently-dumped copy of a large ROM

Two dumps of the same game can still differ by a few bytes depending on the tool that created them. For big NDS files especially, use the exact source the patch author mentions.

Assuming every .xdelta file behaves the same way

xdelta patches can optionally use secondary compression on top of the diff itself. Most ROM hacking patches don't, but it isn't guaranteed by the file extension alone.

Troubleshooting

Patch fails with a "secondary decompressor" or similar error

Some xdelta encoders can enable an extra compression pass on top of the base diff. Browser-based xdelta/VCDIFF decoders commonly support the plain, uncompressed form used by most ROM hacking patches, but not every optional variant. If this happens, check whether the hack offers a patch built without that option.

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It's taking a long time with no visible progress

Large NDS ROMs can run from around 32MB up past 512MB. Reading and hashing a file that size takes real time in a browser — that's expected, not a sign it's stuck.

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Patch applies but the game doesn't boot

Confirm your source ROM byte-for-byte matches what the patch was built against — xdelta diffs are extremely sensitive to any difference in the input file.

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FAQ

No — xdelta is a general-purpose binary diff tool. The ROM hacking community adopted it because it copes well with very large files, not because it was designed for ROMs specifically.
NDS ROMs run much larger than earlier handheld games, often tens to hundreds of megabytes. Formats built for smaller ROMs either can't address that much data or become impractically large as diffs.
The most common cause is a base ROM that doesn't match exactly. A less common cause is a patch built with optional secondary compression that a particular decoder doesn't support.
Yes, though it takes longer than a small GBA or SNES file. The trade-off for staying entirely client-side is that your browser does the same work a desktop tool would.

Related Guides

ROM PatcherPatch a ROM file directly in your browser.Patch Formats ExplainedIPS vs UPS vs BPS vs xdelta — which one do you need?NDS ROM Patcherxdelta is the dominant patch format for Nintendo DS ROM hacks.TroubleshootingFix common ROM patching errors and mismatches.

Large file, same privacy guarantee — your ROM and patch stay on this device the whole time.

Open the ROM Patcher

New to patching in general? See how xdelta compares to IPS, UPS, and BPS.

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