FlexSim MCP Server

Instructions

Implementation Reference

• mcp_server/flexsim_mcp.py:246-254 (handler)

  Main handler implementation of flexsim_reset tool. Uses @mcp.tool() decorator for registration, gets the FlexSim controller, calls reset() to reset simulation to time 0, and returns a success message with error handling.

  @mcp.tool()
  async def flexsim_reset() -> str:
      """Reset simulation to initial state (time = 0)."""
      try:
          controller = await get_controller()
          controller.reset()
          return "✓ Simulation reset to time 0"
      except Exception as e:
          return format_error(e)

• mcp_server/flexsim_mcp.py:147-154 (helper)

  Helper function get_controller() that manages the global FlexSim controller instance with lazy initialization and thread-safe locking.

  async def get_controller():
      """Get or create the FlexSim controller instance."""
      global _controller
  
      async with _controller_lock:
          if _controller is None:
              _controller = await launch_flexsim()
          return _controller

• mcp_server/flexsim_mcp.py:129-140 (helper)

  Helper function format_error() that converts exceptions into user-friendly error messages for display.

  def format_error(e: Exception) -> str:
      """Format exception as user-friendly error message."""
      msg = str(e)
      if "not found" in msg.lower():
          return f"Not found: {msg}"
      elif "syntax" in msg.lower():
          return f"FlexScript syntax error: {msg}"
      elif "license" in msg.lower():
          return f"License error: {msg}"
      elif "permission" in msg.lower():
          return f"Permission denied: {msg}"
      return f"Error: {msg}"

• tests/integration/test_mcp_client.py:269-298 (registration)

  Test code that validates flexsim_reset tool is registered and tests its execution as part of the integration test suite.

  required_tools = ["flexsim_open_model", "flexsim_reset", "flexsim_run",
                   "flexsim_stop", "flexsim_get_time"]
  for tool in required_tools:
      if tool not in tool_names:
          print(f"\nERROR: {tool} tool not found!")
          return False
  
  print("\n✓ All required tools found")
  
  # Open model
  print(f"\nOpening model: {test_model}")
  result = await client.call_tool(
      "flexsim_open_model",
      {"model_path": str(test_model)}
  )
  
  if "result" not in result:
      print(f"\n✗ Failed to open model: {result.get('error')}")
      return False
  
  print("✓ Model opened")
  
  # Reset simulation
  print("\nResetting simulation...")
  result = await client.call_tool("flexsim_reset")
  if "result" not in result:
      print(f"\n✗ Failed to reset: {result.get('error')}")
      return False
  
  print("✓ Simulation reset")

• mcp_server/flexsim_mcp.py:216-216 (registration)

  FastMCP server initialization at module level where all @mcp.tool() decorated functions including flexsim_reset are registered with the MCP server.

  mcp = FastMCP("flexsim_mcp", lifespan=lifespan)