How to patch Heartfelt Gold

Five steps from the readme

1. Copy your clean HeartGold (USA) ROM somewhere safe. Do not patch over the only copy.
2. Open RomPatcher.js. It lists VCDiff (.xdelta) support and runs in a phone browser. A desktop xDelta UI build is the fallback if you already have one; the utility page on romhacking.net was behind a browser check when I looked.
3. Set the original .nds as the source ROM.
4. Set Heartfelt-Gold-v1.0.9-Patch.xdelta as the patch.
5. Save a new .nds. Leave the clean ROM untouched.

Apply exactly one patch. The readme says not to stack Heartfelt Gold on any earlier Retiled patch. The file HG-Retiled-v3.bps in the repository is an older visual-only alternative, not a substitute for v1.0.9.

Check the hash before you play

On Windows the readme’s check is Get-FileHash .\xDelta\Heartfelt-Gold-v1.0.9-Patch.xdelta -Algorithm SHA256. On macOS or Linux it is sha256sum on the same file. The expected patch digest is on the download page.

RomPatcher.js shows the ROM’s CRC32, MD5, and SHA-1 before it writes the output, which is useful on a phone where a terminal is awkward.

Saves from an older build

The readme expects in-game saves from earlier Heartfelt builds to load. v1.0.7 notes describe a load, save, and reload check. The v1.0.9 notes do not add a new save test. Keep a backup, match the save filename to the ROM name, and start from the in-game save rather than an old emulator quick-save.

If the patched ROM is a black screen, go to crashing and black screens. For which app can open an .nds, see GBA or NDS.

Next steps

Read the FAQ for save questions and documented changes before deciding which build to keep.