Gearcoleco

Gearcoleco is a very accurate, cross-platform ColecoVision 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

• Very accurate Z80 core, TMS9918 VDP, SN76489 PSG and AY-3-8910 SGM emulation.
• Support for ColecoVision Super Game Module (SGM) and MegaCart ROMs.
• Support for Super Action Controller (SAC), Wheel Controller and Roller Controller.
• Save states with preview and rewind support.
• Run-ahead support to reduce input latency.
• Compressed ROM support (ZIP).
• 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 registers, tiles, sprites and backgrounds.
• 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, Linux and macOS 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

• BIOS: Gearcoleco needs a BIOS to run. It is possible to load any BIOS but the original one with md5 2c66f5911e5b42b8ebe113403548eee7 is recommended.
• Spinners: When using any kind of spinner it is useful to capture the mouse by pressing F12. It is also recommended to disable spinners for software that don't use them.
• Rewind: Hold the configured rewind hotkey (Backspace by default) or a mapped gamepad shortcut to step backwards through recent gameplay.
• Overscan: For a precise representation of the original image, select Overscan Top+Bottom and Aspect Ratio Standard (4:3 DAR) in the Video menu.
• 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. On macOS, place the file next to the .app bundle.

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.rom it tries to load path_to_rom_file.sym. You can also load a symbol file using the GUI or the CLI. It supports SDCC/NoICE (.noi), wla-dx and vasm/generic file formats.
• Rewind Scrubbing: In debug mode, pause emulation and open the Rewind window to scrub through captured snapshots.

Command Line Usage

gearcoleco [options] [rom_file] [symbol_file]

Arguments:
  [rom_file]               ROM file: accepts ROMs (.col, .cv, .rom, .bin) 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-router         Enable compact MCP tool routing
      --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

Gearcoleco 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. STDIO and HTTP transports are supported, with STDIO preferred.

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

Agent Skills

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

• **[gearcolec