Write codes only for games the user owns or legally obtained, or for their own homebrew. Never download or generate a BIOS, a game image, or keys.
Key each file or entry to the exact executable: PCSX2 serial and CRC, DuckStation serial (plus the hash for a revision with different offsets), Dolphin game ID (plus r<rev>), RPCS3 executable hash, PPSSPP disc ID. Addresses differ between regions and revisions, so a code for one is wrong for another. Ask for the ID or the log line that shows it.
Check every file with a tool before booting, because loaders drop a bad line with only a log message, or none (Dolphin OnFrame). Run python3 scripts/check_pnach.py FILE for .pnach and chtdb's validate_file.py for .cht. For other formats, read the log after loading.
Test one code at a time from a cold boot, with every other code, cheat, and texture pack off. Do not load a save state to test, because it skips the code paths that run at boot.
Quote the log line or the in-game result that shows a code applied. A clean load is not proof.
Say that RetroAchievements hardcore mode disables cheats (and in PCSX2, patch files on disk), so turn it off before testing.
Edit an emulator's settings only while it is stopped, and use only keys the same release wrote.
Never clone, read, build, or modify DuckStation source. Its repository CLAUDE.md forbids AI assistants from operating on it. Writing .cht files and editing a release's settings.ini is fine.
Before any upstream contribution of a patch, apply that project's AI policy:
- PCSX2 AGENTS.md: never create an issue or a PR, and disclose AI use with (AI-assisted). Bundled patches come from pcsx2_patches.
- Dolphin Contributing.md: contributions only from humans, and no LLM use for changes to console behavior. Do not draft a GameSettings change.
- RPCS3, PPSSPP, and xemu: AI-assisted PRs need a disclosure. The human sends all communication.
- DuckStation: patches go by email or Discord. chtdb takes .cht files.

Workflow

Identify the emulator, its release or commit, the game ID, and the region and revision. Read the emulator's reference below.
Find or confirm the addresses from the user's own memory search or disassembly. Do not invent addresses or copy them from another revision.
Write the code in that emulator's grammar, in the user directory, not in bundled defaults.
Run the checker for the format. Fix every error and read every warning.
Enable the code (settings or the per-game list), boot cold with only this code on, and read the log for a load error or an applied line.
Report the file path, the ID it is keyed to, the checker result, and the log line or in-game result.

xemu has no patch or cheat system in its source or docs. For an Xbox game, say so and suggest memory edits through its QEMU monitor or GDB stub ($debug-game-in-emulator).

Scripts

On Windows, use py -3 for python3.
python3 scripts/check_pnach.py FILE... [--json] [--limit N] reports the errors and warnings PCSX2's patch loader would raise. Exit 0 no errors, 1 errors, 2 usage or unreadable input.
python3 scripts/check_settings_keys.py FILE... [--keys LIST] checks a DuckStation settings.ini against the keys release 0.1-11826 wrote: typos, duplicates, and non-boolean values. Exit 0 clean, 1 findings, 2 usage or unreadable input.
scripts/testdata/pnach/: good, warn, and bad .pnach samples for the checker's tests.

References

Emulator	Reference
PCSX2 (PS2) `.pnach`	`references/pcsx2-pnach.md`
DuckStation (PS1) `.cht`	`references/duckstation-cht.md`
Dolphin (GameCube, Wii)	`references/dolphin.md`
RPCS3 (PS3) `patch.yml`	`references/rpcs3.md`
PPSSPP (PSP) CWCheat	`references/ppsspp-cwcheat.md`
Settings files, OpenEmu	`references/frontend-config.md`

For crashes, boot failures, renderer bugs, or stepping guest code, use $debug-game-in-emulator.

write-emulator-patches

Write Emulator Patches

Rules