FourShades
Game Boy emulator · C++20 · 2026 – present
A Game Boy emulator written with AI coding agents, spec-first and test-first, and measured against the public Game Boy test ROMs. The pass rate is the scoreboard, and every number gets published — up or down.
The point is not another emulator; there are hundreds, and better ones. The point is a fixed, respected yardstick for what disciplined agentic development can actually do on hard low-level code.
cpu instructions 499 / 500
test roms 85 / 165
Posts about FourShades
499 out of 500, on purpose
The CPU passes every SingleStepTests instruction but one. The one it fails, it fails deliberately.
Starting the scoreboard at zero
Why I am building a Game Boy emulator in C++ with AI agents, and publishing every number.