LLDB MCP Server

Instructions

Watch types:
- 'write': Break when value is written (modified)
- 'read': Break when value is read
- 'read_write': Break on any access

Args:
    params: WatchpointInput with variable and access type

Returns:
    str: Confirmation of watchpoint creation

Implementation Reference

• lldb_mcp_server.py:1060-1093 (handler)

  The handler function for the 'lldb_watchpoint' tool. It constructs LLDB commands to create a target, set a watchpoint on the specified variable with the given watch type and optional condition, lists the watchpoints, executes them using _run_lldb_script, and formats the output.

  async def lldb_watchpoint(params: WatchpointInput) -> str:
      """Set a watchpoint to break when a variable is accessed.
  
      Watch types:
      - 'write': Break when value is written (modified)
      - 'read': Break when value is read
      - 'read_write': Break on any access
  
      Args:
          params: WatchpointInput with variable and access type
  
      Returns:
          str: Confirmation of watchpoint creation
      """
      commands = [f"target create {params.executable}"]
  
      wp_cmd = f"watchpoint set variable {params.variable}"
  
      if params.watch_type == "read":
          wp_cmd += " --watch read"
      elif params.watch_type == "read_write":
          wp_cmd += " --watch read_write"
      # Default is write
  
      commands.append(wp_cmd)
  
      if params.condition:
          commands.append(f"watchpoint modify --condition '{params.condition}'")
  
      commands.append("watchpoint list")
  
      result = _run_lldb_script(commands)
  
      return f"## Watchpoint on `{params.variable}`\n\n```\n{result['output'].strip()}\n```"

• lldb_mcp_server.py:364-377 (schema)

  Pydantic BaseModel defining the input parameters for the lldb_watchpoint tool, including executable path, variable to watch, watch type, and optional condition.

  class WatchpointInput(BaseModel):
      """Input for setting watchpoints."""
  
      model_config = ConfigDict(str_strip_whitespace=True)
  
      executable: str = Field(..., description="Path to the executable", min_length=1)
      variable: str = Field(..., description="Variable name or memory address to watch", min_length=1)
      watch_type: str = Field(
          default="write", description="Type of access to watch: 'write', 'read', 'read_write'"
      )
      condition: str | None = Field(
          default=None, description="Conditional expression for the watchpoint"
      )

• lldb_mcp_server.py:1050-1059 (registration)

  MCP tool registration decorator that registers the lldb_watchpoint handler function with the FastMCP server, including name and annotations for the tool.

  @mcp.tool(
      name="lldb_watchpoint",
      annotations={
          "title": "Set Watchpoint",
          "readOnlyHint": False,
          "destructiveHint": False,
          "idempotentHint": False,
          "openWorldHint": False,
      },
  )