Gearboy

Gearboy is a cross-platform Game Boy / Game Boy Color emulator written in C++ that runs on Windows, macOS, Linux, BSD and RetroArch, with an embedded MCP server for debugging and tooling.

This is an open source project with its ongoing development made possible thanks to the support by these awesome backers. If you find it useful, please consider sponsoring.

Don't hesitate to report bugs or ask for new features by opening an issue.

Downloads

Notes:

• Windows: May need Visual C++ Redistributable and OpenGL Compatibility Pack
• Linux: May need libsdl3

Features

• Supported cartridges: ROM, ROM + RAM, MBC1, MBC2, MBC3 + RTC, MBC5, HuC-1 and MBC1M (multicart).
• Accurate LCD controller emulation with correct timings and priorities including mid-scanline effects.
• Game Boy Color support.
• LCD screen ghosting effect as seen in the original Game Boy.
• LCD dot matrix effect.
• Battery powered RAM save support.
• Save states.
• Compressed rom support (ZIP).
• Bootrom (BIOS) support.
• Game Genie and GameShark cheat support.
• VGM recorder.
• Supported platforms (standalone): Windows, Linux, BSD and macOS.
• Supported platforms (libretro): Windows, Linux, macOS, Raspberry Pi, Android, iOS, tvOS, PlayStation Vita, PlayStation 3, Nintendo 3DS, Nintendo GameCube, Nintendo Wii, Nintendo WiiU, Nintendo Switch, Emscripten, Classic Mini systems (NES, SNES, C64, ...), OpenDingux, RetroFW and QNX.
• Full debugger with just-in-time disassembler, CPU breakpoints, memory access breakpoints, code navigation (goto address, JP JR and CALL double clicking), debug symbols, automatic labels, memory editor, trace logger, IO inspector and VRAM viewer including tiles, sprites, backgrounds and palettes.
• MCP server for AI-assisted debugging with GitHub Copilot, Claude, ChatGPT and similar, exposing tools for execution control, memory inspection, hardware status, and more.
• Windows and Linux Portable Mode.
• ROM loading from the command line by adding the ROM path as an argument.
• ROM loading using drag & drop.
• Support for modern game controllers through gamecontrollerdb.txt file located in the same directory as the application binary.

Tips

Basic Usage

• Boot ROM: Gearboy can run with or without a Boot ROM. You can optionally load a Boot ROM and enable it.
• Mouse Cursor: Automatically hides when hovering over the main output window or when Main Menu is disabled.
• Portable Mode: Create an empty file named portable.ini in the same directory as the application binary to enable portable mode.

Debugging Features

• Docking Windows: In debug mode, you can dock windows together by pressing SHIFT and dragging a window onto another.
• Multi-viewport: In Windows or macOS, you can enable "multi-viewport" in the debug menu. You must restart the emulator for the change to take effect. Once enabled, you can drag debugger windows outside the main window.
• Single Instance: You can enable "Single Instance" in the Emulator menu. When enabled, opening a ROM while another instance is running will send the ROM to the running instance instead of starting a new one.
• Debug Symbols: The emulator automatically tries to load a symbol file when loading a ROM (.sym, .noi). For example, for path_to_rom_file.gb it tries to load path_to_rom_file.sym. You can also load a symbol file using the GUI or the CLI. It supports RGBDS, GBDK-2020, WLA-DX, no$gmb, SDCC/NoICE (.noi), EQU and generic file formats.

Command Line Usage

gearboy [options] [rom_file] [symbol_file]

Arguments:
  [rom_file]               ROM file: accepts ROMs (.gb, .dmg, .gbc, .cgb, .sgb) or ZIP (.zip)
  [symbol_file]            Optional symbol file for debugging

Options:
  -f, --fullscreen         Start in fullscreen mode
  -w, --windowed           Start in windowed mode with menu visible
      --mcp-stdio          Auto-start MCP server with stdio transport
      --mcp-http           Auto-start MCP server with HTTP transport
      --mcp-http-port N    HTTP port for MCP server (default: 7777)
      --headless           Run without GUI (requires --mcp-stdio or --mcp-http)
  -v, --version            Display version information
  -h, --help               Display this help message

MCP Server

Gearboy includes a Model Context Protocol (MCP) server that enables AI-assisted debugging through AI agents like GitHub Copilot, Claude, ChatGPT and similar. The server provides tools for execution control, memory inspection, breakpoints, disassembly, hardware status, and more.

For complete setup instructions and tool documentation, see MCP_README.md.

Agent Skills

Gearboy provides Agent Skills that teach AI assistants how to effectively use the emulator for specific tasks:

• gearboy-debugging — Game debugging, code tracing, breakpoint management, hardware inspection, and reverse engineering.
• gearboy-romhacking — Cheat creation, memory searching, ROM data modification, text translation, and game patching.

Install with npx skills add drhelius/gearboy. See the skills README for details.

Build Instructions

Windows

• Install Microsoft Visual Studio Community 2022 or later.
• Download the latest SDL3 VC development libraries from SDL3 Releases (the file named SDL3-devel-x.y.z-VC.zip).
• Extract the archive and rename the resulting folder (e.g. SDL3-x.y.z) to SDL3.
• Place the SDL3 folder inside platforms/windows/dependencies/ so that the include path is platforms/windows/dependencies/SDL3/include/SDL3/.
• Open the Gearboy Visual Studio solution platforms/windows/Gearboy.sln and build.

macOS

• Install Xcode and run xcode-select --install in the terminal for the compiler to be available on the command line.
• Run these commands to generate a Mac app bundle:

brew install sdl3
cd platfor