Universal Checksum Patcher

Patches Paradox game executables so mods that change the checksum still allow achievements and ironman. It flips the executable's "game is unmodified" check — the same edit the Ghidra guides make by hand, done automatically and resilient to updates.

It does not enable the console, cheats, or achievement-disabling game rules.

Supported games

No Linux/macOS builds.

Install & use

1. Download universal-checksum-patcher.exe from Releases.
2. Put it next to the game exe and run it, or drag the exe onto it:
3. HoI4 / EU4: next to hoi4.exe / eu4.exe (Steam → Manage → Browse local files).
4. EU5: the exe is in the binaries\ subfolder. Drop the patcher in the game root or in binaries\; it scans one level of subfolders.
5. Under C:\Program Files, right-click → Run as administrator. Writing there needs elevation; the tool says so if it hits a permission error.
6. Pick Patch. A .backup of the original is saved automatically.

Re-run after every game update — an update replaces the exe with an unpatched one.

Restore reverts to the original. Also scriptable: universal-checksum-patcher.exe patch / restore / status.

How it works

It locates the check by a wildcard byte pattern anchored to a stable engine string (e.g. HoI4's Active Mod Count:) rather than an absolute address, so game updates don't break the match. Matches are confined to real functions via the .pdata exception table. The patch is transactional: it verifies the exact bytes, backs up the original, writes atomically, re-checks the file didn't change mid-run, and refuses ambiguous matches. Running twice is a no-op.

Signatures live in internal/core/signatures.json (embedded). Override them without rebuilding by dropping a signatures.json next to the exe.

Build from source

make build   # cross-compiles the Windows exe (amd64) into build/
make test    # runs unit tests

Requires Go 1.24+.

Credits

Method based on the community Ghidra guide How to Play with Mods and Get Achievements; EU5 patterns cross-checked against UFOdestiny/EU5-Patcher.