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Gearsystem MCP Server

A Model Context Protocol server for the Gearsystem emulator, enabling AI-assisted debugging and development of Sega Master System / Game Gear / SG-1000 games.

This server provides tools for game development, rom hacking, reverse engineering, and debugging through standardized MCP protocols compatible with AI agents like GitHub Copilot, Claude, Codex and others.

Downloads

Platform Architecture Download Link
Windows x64 Gearsystem-3.9.13-mcpb-windows-x64.mcpb
ARM64 Gearsystem-3.9.13-mcpb-windows-arm64.mcpb
macOS x64 Gearsystem-3.9.13-mcpb-macos-x64.mcpb
ARM64 Gearsystem-3.9.13-mcpb-macos-arm64.mcpb
Linux x64 Gearsystem-3.9.13-mcpb-linux-x64.mcpb
ARM64 Gearsystem-3.9.13-mcpb-linux-arm64.mcpb

Features

  • Full Debugger Access: CPU registers, memory inspection, breakpoints, and execution control
  • Multiple Memory Areas: Access RAM, VRAM, CRAM, ROM banks, external RAM, BIOS, and more
  • Disassembly: View disassembled Z80 code around PC or any address
  • Hardware Inspection: Z80 CPU, VDP, PSG, YM2413 FM synthesis
  • Sprite Viewer: List and inspect all 64 sprites with images
  • Symbol Support: Add, remove, list, and look up debug symbols
  • Input State: Inspect effective pressed buttons and pending tap releases
  • Bookmarks: Memory and disassembler bookmarks for navigation
  • Call Stack: View function call hierarchy
  • Trace Logger: CPU instruction trace with interleaved hardware events (VDP, PSG, YM2413, I/O, bank switching)
  • Rewind: Time-travel debugging with snapshot status and seek tools
  • Screenshot Capture: Get current frame as PNG image
  • GUI Integration: MCP server runs alongside the emulator GUI, sharing the same state

Transport Modes

The Gearsystem MCP server supports two transport modes:

STDIO Transport (Recommended)

The default mode uses standard input/output for communication. The emulator is launched by the AI client and communicates through stdin/stdout pipes.

HTTP Transport

The HTTP transport mode runs the emulator with an embedded web server on 127.0.0.1:7777/mcp by default. The emulator stays running independently while the AI client connects via HTTP. Each request's Host and browser Origin must match the address on which its connection reached the server. Loopback mode can run without authentication; wildcard and other non-loopback bind addresses require GEARSYSTEM_MCP_HTTP_TOKEN, and the server refuses to start without it.

Headless Mode

Add --headless to run without a GUI window. This is useful for servers, CLI agents, or any machine without a display. All MCP tools work identically in headless mode. Requires --mcp-stdio or --mcp-http.

MCP Tool Router

By default, Gearsystem exposes every MCP tool directly. This avoids nested tool discovery in clients that already defer MCP schemas, including Claude Code.

Add --mcp-router to expose a compact set of high-frequency tools directly and route advanced debugger tools through lightweight discovery tools. This reduces MCP context while preserving access to the full debugger surface.

Direct tools in routed mode: load_media, get_media_info, debug_pause, debug_continue, debug_step_into, get_z80_status, read_memory, write_memory, get_disassembly, set_breakpoint, get_screenshot, and controller_button.

Router tools:

  • list_tool_categories lists routed tool categories with descriptions and tool counts.
  • get_category_tools lists routed tools in a category with compact descriptions.
  • search_tools searches direct and routed tools and returns compact category/tool/description matches.
  • get_tool_info returns one tool's real input schema and metadata.
  • execute_tool executes a routed tool by name. First use search_tools or get_category_tools to discover the tool, then call get_tool_info to obtain its exact input schema.

Example routed call:

{
  "name": "get_vdp_status",
  "arguments": {}
}

Without --mcp-router, call every MCP tool directly.

Quick Start

STDIO Mode with VS Code

  1. Install GitHub Copilot extension in VS Code

  2. Configure VS Code settings:

    Add to your workspace folder a file named .vscode/mcp.json with:

    {
  "servers": {
    "gearsystem": {
      "command": "/path/to/gearsystem",
      "args": ["--mcp-stdio"]
    }
  }
}

    Important: Update the command path to match your build location:

    • macOS: /path/to/gearsystem
    • Linux: /path/to/gearsystem
    • Windows: C:/path/to/gearsystem.exe

  3. Restart VS Code may be necessary for settings to take effect

  4. Open GitHub Copilot Chat and start debugging:

    • The emulator will auto-start with MCP server enabled
    • Load a game ROM
    • Start chatting with Copilot about the game state

STDIO Mode with Claude Desktop

Option 1: Desktop Extension (Recommended)

The easiest way to install Gearsystem MCP server on Claude Desktop is using the MCPB package:

  1. Download the latest MCPB package for your platform from the releases page.

  2. Install the extension:

    • Open Claude Desktop
    • Navigate to Settings > Extensions
    • Click Advanced settings
    • In the Extension Developer section, click Install Extension…
    • Select the downloaded .mcpb file

  3. Start debugging: The extension is now available in your conversations. The emulator will automatically launch when the tool is enabled.

Option 2: Manual Configuration

If you prefer to build from source or configure manually:

  1. Edit Claude Desktop config file:

    Follow these instructions to access Claude's config file, then edit it to include:

    {
  "mcpServers": {
    "gearsystem": {
      "command": "/path/to/gearsystem/platforms/macos/gearsystem",
      "args": ["--mcp-stdio"]
    }
  }
}

    Config file locations:

    • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
    • Windows: %APPDATA%\Claude\claude_desktop_config.json
    • Linux: ~/.config/Claude/claude_desktop_config.json

    Important: Update the command path to match your build location.

  2. Restart Claude Desktop

STDIO Mode with Claude Code

  1. Add the Gearsystem MCP server using the CLI:

    claude mcp add --transport stdio gearsystem -- /path/to/gearsystem --mcp-stdio

    Important: Update the path to match your build location.

  2. Verify the server was added:

    claude mcp list

  3. Start debugging: Open Claude Code and start chatting about the game state. The emulator will auto-start when tools are invoked.

HTTP Mode

  1. Start the emulator manually with HTTP transport:

    ./gearsystem --mcp-http

The default endpoint is `http://127.0.0.1:7777/mcp`.

To use a custom port:

```bash
 ./gearsystem --mcp-http --mcp-http-port 3000

To bind to a custom address, set a bearer token first:

GEARSYSTEM_MCP_HTTP_TOKEN="change-this-token" ./gearsystem --mcp-http --mcp-http-address 0.0.0.0 --mcp-http-port 3000

Clients must connect using the server's actual interface address, such as http://192.168.1.50:3000/mcp, not 0.0.0.0 or a spoofed loopback address.

You can also start the server using the "MCP" menu in the GUI.

  1. Configure bearer-token authentication:

Set GEARSYSTEM_MCP_HTTP_TOKEN before starting HTTP mode. Authentication is optional for loopback binds and required for wildcard or other non-loopback binds.

macOS and Linux:

GEARSYSTEM_MCP_HTTP_TOKEN="change-this-token" ./gearsystem --mcp-http

Windows PowerShell:

$env:GEARSYSTEM_MCP_HTTP_TOKEN = "change-this-token"
.\gearsystem.exe --mcp-http

Windows Command Prompt:

set GEARSYSTEM_MCP_HTTP_TOKEN=change-this-token
gearsystem.exe --mcp-http

  1. Configure VS Code .vscode/mcp.json:

    {
  "servers": {
    "gearsystem": {
      "type": "http",
      "url": "http://127.0.0.1:7777/mcp",
      "headers": {
        "Authorization": "Bearer change-this-token"
      }
    }
  }
}

  2. Or configure Claude Desktop:

    {
  "mcpServers": {
    "gearsystem": {
      "type": "http",
      "url": "http://127.0.0.1:7777/mcp",
      "headers": {
        "Authorization": "Bearer change-this-token"
      }
    }
  }
}

  3. Or configure Claude Code:

    

    4. 



claude mcp add --transport http gearsystem http://127.0.0.1:7777/mcp



6. **Restart your AI client** and start debugging

> **Note:** The MCP HTTP Server must be running standalone before connecting the AI client.
> **Security:** Without `GEARSYSTEM_MCP_HTTP_TOKEN`, HTTP mode starts only on a loopback address. Wildcard and other non-loopback binds are refused. `Host` and browser `Origin` values are matched to the connection's actual destination address to prevent DNS rebinding and address spoofing.

## Usage Examples

Once configured, you can ask your AI assistant:

### Basic Commands

- "What game is currently loaded?"
- "Load the ROM at /path/to/game.sms"
- "Show me the current CPU registers"
- "Read 16 bytes from RAM starting at 0xC000"
- "Set a breakpoint at address 0x0066"
- "Pause execution and show me all sprites"
- "Step through the next 5 instructions"
- "Capture a screenshot of the current frame"
- "Tap the up button on player 1 controller"

### Advanced Debugging Workflows

- "Find the VBlank interrupt handler, analyze what it does, and add symbols for all the subroutines it calls"
- "Locate the sprite update routine. Study how this game manages its sprite system, explain the algorithm, and add bookmarks to key sections. Also add watches for any sprite-related variables you find"
- "There's a data decompression routine around address 0x8000. Step through it instruction by instruction, reverse engineer the compression algorithm, and explain how it works with examples"
- "Find where the game stores its level data in ROM. Analyze the data structure format, create a memory map showing each section, and add symbols for the data tables"
- "The game is rendering corrupted graphics. Examine the VDP registers, check the VRAM contents, inspect the sprite attribute table, and diagnose what's causing the corruption. Set up watches on relevant memory addresses"

## Available MCP Tools

This is the full tool catalog. All tools are exposed directly by default. With `--mcp-router`, discover advanced tools through `search_tools` or `get_category_tools`, inspect their schemas with `get_tool_info`, then invoke them with `execute_tool`.

The server exposes tools organized in the following categories:

### Execution Control
- `debug_pause` - Pause emulation
- `debug_continue` - Resume emulation
- `debug_step_into` - Step one Z80 instruction
- `debug_step_over` - Step over subroutine calls
- `debug_step_out` - Step out of current subroutine
- `debug_step_frame` - Step one or more frames
- `debug_run_to_cursor` - Continue execution until reaching specified address
- `debug_reset` - Reset emulation
- `debug_get_status` - Get debug status (paused, at_breakpoint, pc address)

### CPU & Registers
- `write_z80_register` - Set register value (AF, BC, DE, HL, AF', BC', DE', HL', IX, IY, SP, PC, WZ, A, F, B, C, D, E, H, L, I, R)
- `get_z80_status` - Get complete Z80 CPU status (registers, flags, interrupts, halt, interrupt mode)

### Memory Operations
- `list_memory_areas` - List all available memory areas
- `read_memory` - Read from specific memory area
- `write_memory` - Write to specific memory area
- `get_memory_selection` - Get current memory selection range
- `select_memory_range` - Select a range of memory addresses
- `set_memory_selection_value` - Set all bytes in selection to specified value
- `add_memory_bookmark` - Add bookmark in memory area
- `remove_memory_bookmark` - Remove memory bookmark
- `list_memory_bookmarks` - List all bookmarks in memory area
- `add_memory_watch` - Add watch (tracked memory location)
- `remove_memory_watch` - Remove memory watch
- `list_memory_watches` - List all watches in memory area
- `memory_search_capture` - Capture memory snapshot for search comparison
- `memory_search` - Search memory with operators (<, >, ==, !=, <=, >=), compare types (previous, value, address), and data types (hex, signed, unsigned)
- `memory_find_bytes` - Find byte sequences in memory

### Disassembly & Debugging
- `get_disassembly` - Get Z80 disassembly for specified address range
- `add_symbol` - Add symbol (label) at specified address
- `remove_symbol` - Remove symbol
- `list_symbols` - List all defined symbols
- `lookup_symbol_by_name` - Find all exact-name symbol matches
- `lookup_symbol_at_address` - Find symbol at bank/address
- `add_disassembler_bookmark` - Add bookmark in disassembler
- `remove_disassembler_bookmark` - Remove disassembler bookmark
- `list_disassembler_bookmarks` - List all disassembler bookmarks
- `get_call_stack` - View function call hierarchy
- `get_trace_log` - Read trace logger entries (CPU + hardware events). Start the trace logger from the debugger window first
- `set_trace_log` - Start or stop trace logging with event filters

### Breakpoints
- `set_breakpoint` - Set execution, read, or write breakpoint (supports 4 memory areas: rom_ram, vram, cram, vdp_reg)
- `set_breakpoint_range` - Set breakpoint for an address range (supports 4 memory areas)
- `remove_breakpoint` - Remove breakpoint
- `list_breakpoints` - List all breakpoints
- `toggle_irq_breakpoints` - Enable or disable breaking on IRQs (RESET, NMI, INT)

### Hardware Status
- `get_vdp_registers` - Get all 11 VDP registers (R0-R10) with hex values and descriptions
- `get_vdp_status` - Get VDP status (flags, counters, mode, SG-1000 mode, extended mode 224)
- `get_psg_status` - Get SN76489 PSG status for all 4 channels (3 tone + 1 noise): volume, period, frequency, GG stereo
- `get_ym2413_status` - Get YM2413 FM synth status: 9 channels, instruments, key-on, f-number, block, envelope, rhythm mode, user instrument

### Sprites
- `list_sprites` - List all 64 sprites with position, size, pattern index
- `get_sprite_image` - Get sprite image as base64 PNG

### Screen Capture
- `get_screenshot` - Capture current screen frame as base64 PNG

### Media & State Management
- `get_media_info` - Get loaded ROM info (file path, type, size, mapper, zone, system)
- `list_recent_media` - List the 10 most recent ROM files opened by Gearsystem
- `load_media` - Load ROM file (.sms, .gg, .sg, .zip). Automatically loads .sym symbol file if present
- `load_symbols` - Load debug symbols from file (.sym format with 'BANK:ADDRESS LABEL' entries)
- `list_save_state_slots` - List all 5 save state slots with information (rom name, timestamp, validity)
- `select_save_state_slot` - Select active save state slot (1-5) for save/load operations
- `save_state` - Save emulator state to currently selected slot
- `load_state` - Load emulator state from currently selected slot
- `save_state_file` - Save emulator state to an explicit file path
- `load_state_file` - Load emulator state from an explicit file path
- `set_fast_forward_speed` - Set fast forward speed multiplier (0: 1.5x, 1: 2x, 2: 2.5x, 3: 3x, 4: Unlimited)
- `toggle_fast_forward` - Toggle fast forward mode on/off
- `get_rewind_status` - Get rewind buffer status (enabled, snapshots, capacity, buffered seconds)
- `rewind_seek` - Seek to a specific rewind snapshot while paused

### Controller Input
- `controller_button` - Control a button on a controller (player 1-2). Use action 'press' to hold the button, 'release' to let it go, or 'press_and_release' to simulate a quick tap. Buttons: up, down, left, right, 1, 2, start
- `controller_macro` - Run an ordered input macro. Top-level `player` defaults to 1, and each command may override it. Supported commands are `tap`, `press`, `release`, and `wait`; timing is explicit through `wait` frame counts
- `get_input_state` - Get effective pressed buttons and pending tap releases

## How MCP Works in Gearsystem

- The MCP server runs **alongside** the GUI in a background thread
- The emulator GUI remains fully functional (you can play/debug normally while using MCP)
- Commands from the AI are queued and executed on the GUI thread
- Both GUI and MCP share the same emulator state
- Changes made through MCP are instantly reflected in the GUI and vice versa

## Architecture

### STDIO Transport



┌─────────────────┐                    ┌──────────────────┐
│   VS Code /     │       stdio        │   Gearsystem     │
│ Claude Desktop  │◄──────────────────►│    MCP Server    │
│   (AI Client)   │       pipes        │  (background)    │
└─────────────────┘                    └──────────────────┘
│                                       │
└───► Launches ►────────────────────────┘
│
│ Shared State
▼
┌──────────────────┐
│   Emulator Core  │
│   + GUI Window   │
└──────────────────┘



### HTTP Transport



┌─────────────────┐                    ┌──────────────────┐
│   VS Code /     │  HTTP (port 7777)  │   Gearsystem     │
│ Claude Desktop  │◄──────────────────►│ MCP HTTP Server  │
│   (AI Client)   │                    │    (listener)    │
└─────────────────┘                    └──────────────────┘
│
│ Shared State
▼
┌──────────────────┐
│   Emulator Core  │
│   + GUI Window   │
└──────────────────┘