Frequently asked questions
Common questions about ROM patching and about how this site works. The short version: ten patch formats are supported, nothing you select is ever uploaded, and a failing patch almost always means the base ROM is not the one the patch expects.
Frequently asked questions
What is a ROM patcher?
A ROM patcher applies a patch file to a game ROM, turning it into a modified version such as a fan translation, a romhack or a bug fix. The patch contains only the differences, so you supply your own ROM and the patcher reconstructs the modified game on your device.
Are my ROMs uploaded to a server?
No. Everything runs in your browser using JavaScript and Web Workers. Your ROM and patch are read into memory on your own device and never transmitted. You can load the page, disconnect from the internet, and patching still works.
Which patch formats are supported?
IPS, BPS, UPS, APS in both its N64 and GBA variants, RUP, PPF, BSDiff, xdelta/VCDIFF, EBP and Star Rod .mod files. You can create patches in IPS, BPS, UPS, APS, RUP, PPF and EBP.
Do I need to install anything?
No. There is nothing to download and no account to create. The patcher is a web page that does its work locally, so it runs on Windows, macOS, Linux, ChromeOS, Android and iOS equally.
Why does my patch say the checksum does not match?
Your base ROM is not the exact file the patch was built from. The usual causes are a copier header on a SNES or NES ROM, a different regional release or revision, or a ROM that has already been patched. Formats like BPS check this deliberately so you do not end up with a corrupt game.
Do you host ROMs?
No, and we do not link to them. This site provides patching tools only. You supply your own ROM, and the lawful way to obtain one is to dump it from a cartridge or disc you own.
Can I patch a ROM on my phone?
Yes. The patcher works in mobile Safari and Chrome, and the patched ROM saves to your Downloads folder. Cartridge ROMs are no problem. Large disc images can exceed the memory a phone browser is allowed, so those are better done on a computer.
Do I need to unzip the patch first?
No. Select the zip and the patcher extracts the patch inside. If an archive contains several patches, you get a list to choose from. Only zip is handled, so extract .rar and .7z files first.
Will patching modify my original ROM?
No. The original file is only ever read. The patched ROM is built in memory and saved as a separate download, so you can always patch again from the same clean copy.
Is it legal to use a ROM patcher?
The tool itself is an ordinary file utility. Patches are generally distributed freely because they contain only the author’s own changes rather than the copyrighted game. Where you stand on the ROM itself depends on how you obtained it and on the law where you live.
What is the difference between IPS and BPS?
IPS is a simple list of byte overwrites with a 16 MB ceiling and no verification. BPS stores a real binary delta, embeds CRC32 checksums so it refuses to patch the wrong ROM, has no practical size limit, and produces much smaller patches. BPS is the better default.
What software is this built on?
The patching engine is Rom Patcher JS by Marc Robledo, an open-source MIT-licensed project. This site vendors it directly from its GitHub repository at build time and verifies it with automated round-trip tests before every deploy.