Gearboy
Gearboy is an accurate, cross-platform Game Boy / Game Boy Color / Super Game Boy 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
- Homebrew: If Homebrew asks you to trust the third-party tap, run
brew trust --tap drhelius/geardome - Linux: May need
libsdl3
Features
- Supported cartridges: ROM, ROM + RAM, MBC1, MBC2, MBC3, MBC5, MBC7, HuC-1, HuC-3, MMM01, Pocket Camera, TAMA5, MBC1M, Wisdom Tree, M161, Sachen MMC1, Sachen MMC2 and PKJD.
- Game Boy Color support.
- Super Game Boy support.
- LCD screen ghosting effect as seen in the original Game Boy.
- LCD dot matrix effects.
- Battery powered RAM save support.
- Save states with preview and rewind support.
- 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, webOS, 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, Codex and similar, exposing tools for execution control, memory inspection, hardware status, rewind and more.
- Windows and Linux Portable Mode.
- Programmable Shader Chain.
- 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.iniin 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
Emulatormenu. 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.gbit tries to loadpath_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-no-router Expose all MCP tools directly
--mcp-http-address A HTTP bind address (default: 127.0.0.1)
--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, Codex and similar. The server provides tools for execution control, memory inspection, breakpoints, disassembly, hardware status, and more. HTTP transport binds to 127.0.0.1 by default, validates Host and browser Origin values against the configured endpoint, and can require bearer-token auth with the GEARBOY_MCP_HTTP_TOKEN environment variable.
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 2