Delta Patcher FAQ

Delta Patcher is a free, open-source desktop program that applies and creates XDelta patches. You give it an original file and a .xdelta patch, and it rebuilds the modified file. It can also compare an original and a modified file and save the differences as a new patch. It’s developed by Marco Calautti, written in C++ with wxWidgets, and has the xdelta3 engine built in. Overview of Delta Patcher.

An XDelta patch is a file, usually ending in .xdelta, that describes how to turn one specific file into another. Instead of storing the whole new file, it stores instructions such as “copy these bytes from the original” and “add these new bytes.” It uses the VCDIFF format (RFC 3284) as implemented by the xdelta3 tool. What is XDelta?

Yes. Delta Patcher costs nothing and is open-source software under the GNU General Public License v2.0. You can use it, share it and study or modify its source code under that license’s terms.

No. This is an independent guide, not affiliated with the developer. The official project lives on GitHub, and the Linux package is listed on Flathub. Every download link on this site points to those official sources. About this site.

The official builds are published by the developer on GitHub, and the source code is public for anyone to inspect. To be confident in your copy, download it only from the official release and compare its SHA-256 checksum with the values on the download page. Copies from other download sites can’t be vouched for. Because the Windows and macOS builds aren’t signed with a commercial certificate, your system may show a warning on first launch; that alone doesn’t indicate a problem.

Yes. Version 3.1.6 has builds for Windows 7 or later (64-bit and 32-bit), macOS 11 Big Sur or later (one app for Apple silicon and Intel), and Linux: a GTK 3 build for x86-64 with glibc 2.38 or newer, or the Flathub package for x86-64 and ARM64. There’s no Android or iOS version. Installation guide for each system.

No. Since version 3.0.0 the xdelta3 engine is compiled into Delta Patcher as a library (version 3.1.6 uses xdelta3 3.1.0). You don’t need the xdelta3 command-line tool, .NET or any other runtime.

No. The Windows, macOS and Linux downloads are portable: extract the .zip and run the program. It doesn’t save any settings, so removing it is just a matter of deleting it. On Linux you can also install it from Flathub, which handles updates.

Download the latest release (3.1.6) for your system. On Windows, that’s the 64-bit .zip unless your Windows is 32-bit. On older Linux distributions or ARM, use Flathub. For Windows XP or Vista, the last compatible version is 3.0.1. See all downloads.

Open Delta Patcher, click the folder button next to Original file and choose the file to patch, then click the folder button next to XDelta patch and choose the patch. Optionally tick Backup original file in the gear menu, then click Apply patch. Full step-by-step guide.

Any file. XDelta works at the byte level, so it doesn’t matter whether the file is a disc image, a cartridge ROM, a document or a program. What matters is that it’s the exact file the patch was made from. Since version 3.1.5, files larger than 4 GB are supported.

In the same folder as the original; there’s no option to choose another location. With Backup original file off (the default), the patched file replaces the original under the same name. With it on, the original is kept and the result is saved with PATCHED added before the extension, for example GamePATCHED.iso. More about the output file.

Only if the new patch was made for that patched file, such as an update designed to be applied on top of a previous patch. A patch made for the original won’t apply to a patched copy and fails with a checksum error. Keep an untouched original so you can always start again. Fixing already-patched files.

Yes, if the patches are designed to be stacked. Apply them in the order the author specifies, each to the output of the previous one. Patches meant as alternatives (for example, two different translations) can’t be combined this way. How to apply multiple patches.

No. Delta Patcher only supports XDelta (VCDIFF) patches. Other formats need a tool that supports them, and renaming a patch to .xdelta won’t help. Patch formats compared.

Yes. Click the switch-mode button at the bottom right to enter patch creation mode, choose the original file, the modified file and a save location, add an optional description, and click Create patch. How to create an XDelta patch.

Usually because the changed data is compressed or encrypted, so a small edit changes most of the bytes after it. It can also happen if data moved further than the source window (try a larger Src Window Size) or if you selected unrelated files. Why patches get large.

Yes. They’re standard xdelta3 patches. For the widest compatibility, keep secondary compression set to none, because some tools don’t support every compressor. The patch description only appears in Delta Patcher; other tools ignore it.

The most common reason by far is a source file that isn’t exactly the one the patch was made for: a different region, revision, dump or format, or a file that’s already patched. Other causes include a damaged or non-XDelta patch, a folder you can’t write to, and too little disk space. Troubleshoot common errors.

It means the data rebuilt from your source file doesn’t match the checksums stored in the patch, so your source file differs from the author’s. Delta Patcher reports it as “The file you are trying to patch is not the right one”; the log says target window checksum mismatch. How to fix checksum mismatch.

Check that you’re opening the patched file and not the original, that checksum validation was on, and that you followed the patch’s instructions (other patches, emulator settings, renamed files). For disc images, make sure any .cue file points to the patched file’s name. Fixing a patched file that doesn’t work.

No. Turning off validation doesn’t fix a wrong source file; it only removes the check, so the patch produces a corrupt file instead of an error. Find the correct source file instead. Why disabling validation is a bad idea.