Pokémon HeartGold Decompiled to Source Code Using AI in a Month

A developer from Manchester, known as ctrl-cheeb-del, has fully translated the code of Pokémon HeartGold and SoulSilver for Nintendo DS into C and C++ source code using AI agents. Both American versions compile from the generated code byte-for-byte identical to the original ROM files. According to the author, the work took about a month, and the token cost at public API rates amounted to approximately $56,000.

This is about matching decompilation: machine code is translated back into readable source code, which, when compiled with the same original compiler, produces exactly the same binary as on the cartridge. This is an objective verification: if the bytes match, the function is correctly restored.

According to published statistics, AI agents annotated 4,075,354 bytes of ARM9 and ARM7 processor code. Distribution: 97.9 percent pure C, 1.3 percent C++, 0.6 percent original assembly inserts, 0.1 percent generated by build tools.

The work was done in a separate fork of the pokeheartgold repository, which is maintained by the group of enthusiasts pret; its members manually decompile Pokémon, and have been working on HeartGold and SoulSilver since June 2021. The author of the fork explicitly states that all the basic infrastructure belongs to pret, and the group does not accept AI-written code and does not want to be associated with the result. Critics on social media noted that the fork heavily relies on years of others' work and completes the remainder. Previously, in April, there was a similar experiment pokeheartgold-slop.

The $56,000 figure requires clarification: this is the cost of tokens at public rates, not actual expenses. When working through subscriptions like Claude Max, actual costs can be orders of magnitude lower.

HeartGold and SoulSilver were released on the DS in 2009 as remakes of Gold and Silver for the Game Boy Color. Decompilation does not make the game free: the repository contains only the code, a personal dump of the original cartridge is needed for compilation, and graphics, music, and assets are protected by copyright of Nintendo and The Pokémon Company. Nintendo's license agreement also prohibits decompilation.

The main practical benefit is the creation of modifications: with the full source code, it's easier to make hacks, fan games on the fourth-generation engine, PC ports, and study the original's structure. Previously, AI agents helped bring the decompilation of Super Smash Bros. Melee and both parts of Snowboard Kids to full completion, and Maurice Hoymann shared how 15 or more agents recreated the code of Call of Duty in three months, spending over 500 billion tokens.