FlexSim MCP Server

Instructions

Implementation Reference

• mcp_server/flexsim_mcp.py:257-265 (handler)

  The flexsim_run tool handler that starts continuous simulation. Gets the controller and calls controller.run() to start the simulation, returning a success message with a hint to use flexsim_stop to pause.

  @mcp.tool()
  async def flexsim_run() -> str:
      """Start running the simulation continuously."""
      try:
          controller = await get_controller()
          controller.run()
          return "✓ Simulation running (use flexsim_stop to pause)"
      except Exception as e:
          return format_error(e)

• mcp_server/flexsim_mcp.py:257-265 (registration)

  Registration of flexsim_run as an MCP tool using the @mcp.tool() decorator from FastMCP framework.

  @mcp.tool()
  async def flexsim_run() -> str:
      """Start running the simulation continuously."""
      try:
          controller = await get_controller()
          controller.run()
          return "✓ Simulation running (use flexsim_stop to pause)"
      except Exception as e:
          return format_error(e)

• mcp_server/flexsim_mcp.py:119-126 (helper)

  format_time helper function used to format simulation time as human-readable strings (seconds, minutes, hours).

  def format_time(seconds: float) -> str:
      """Format simulation time as human-readable string."""
      if seconds < 60:
          return f"{seconds:.2f}s"
      elif seconds < 3600:
          return f"{seconds/60:.2f}m"
      else:
          return f"{seconds/3600:.2f}h"

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

  format_error helper function that formats exceptions into user-friendly error messages, categorizing errors by type (not found, syntax, license, permission).

  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}"

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

  get_controller helper function that manages the global FlexSim controller instance, creating it lazily on first use via launch_flexsim() with async locking for thread safety.

  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