BlenderMCP

Instructions

Implementation Reference

• src/blender_mcp/server.py:313-329 (handler)

  The handler function for the 'execute_blender_code' tool. It sends the provided Python code to the Blender addon via socket connection for execution and returns the result or error message.
  @mcp.tool() def execute_blender_code(ctx: Context, code: str) -> str: """ Execute arbitrary Python code in Blender. Make sure to do it step-by-step by breaking it into smaller chunks. Parameters: - code: The Python code to execute """ try: # Get the global connection blender = get_blender_connection() result = blender.send_command("execute_code", {"code": code}) return f"Code executed successfully: {result.get('result', '')}" except Exception as e: logger.error(f"Error executing code: {str(e)}") return f"Error executing code: {str(e)}"
• src/blender_mcp/server.py:313-313 (registration)

  The @mcp.tool() decorator registers the execute_blender_code function as an MCP tool.
  @mcp.tool()
• src/blender_mcp/server.py:108-162 (helper)

  The send_command method of BlenderConnection class, used by the handler to communicate the code to Blender.
  def send_command(self, command_type: str, params: Dict[str, Any] = None) -> Dict[str, Any]: """Send a command to Blender and return the response""" if not self.sock and not self.connect(): raise ConnectionError("Not connected to Blender") command = { "type": command_type, "params": params or {} } try: # Log the command being sent logger.info(f"Sending command: {command_type} with params: {params}") # Send the command self.sock.sendall(json.dumps(command).encode('utf-8')) logger.info(f"Command sent, waiting for response...") # Set a timeout for receiving - use the same timeout as in receive_full_response self.sock.settimeout(15.0) # Match the addon's timeout # Receive the response using the improved receive_full_response method response_data = self.receive_full_response(self.sock) logger.info(f"Received {len(response_data)} bytes of data") response = json.loads(response_data.decode('utf-8')) logger.info(f"Response parsed, status: {response.get('status', 'unknown')}") if response.get("status") == "error": logger.error(f"Blender error: {response.get('message')}") raise Exception(response.get("message", "Unknown error from Blender")) return response.get("result", {}) except socket.timeout: logger.error("Socket timeout while waiting for response from Blender") # Don't try to reconnect here - let the get_blender_connection handle reconnection # Just invalidate the current socket so it will be recreated next time self.sock = None raise Exception("Timeout waiting for Blender response - try simplifying your request") except (ConnectionError, BrokenPipeError, ConnectionResetError) as e: logger.error(f"Socket connection error: {str(e)}") self.sock = None raise Exception(f"Connection to Blender lost: {str(e)}") except json.JSONDecodeError as e: logger.error(f"Invalid JSON response from Blender: {str(e)}") # Try to log what was received if 'response_data' in locals() and response_data: logger.error(f"Raw response (first 200 bytes): {response_data[:200]}") raise Exception(f"Invalid response from Blender: {str(e)}") except Exception as e: logger.error(f"Error communicating with Blender: {str(e)}") # Don't try to reconnect here - let the get_blender_connection handle reconnection self.sock = None raise Exception(f"Communication error with Blender: {str(e)}")
• src/blender_mcp/server.py:206-237 (helper)

  Helper function to get or create the persistent socket connection to Blender, called by the handler.
  def get_blender_connection(): """Get or create a persistent Blender connection""" global _blender_connection, _polyhaven_enabled # Add _polyhaven_enabled to globals # If we have an existing connection, check if it's still valid if _blender_connection is not None: try: # First check if PolyHaven is enabled by sending a ping command result = _blender_connection.send_command("get_polyhaven_status") # Store the PolyHaven status globally _polyhaven_enabled = result.get("enabled", False) return _blender_connection except Exception as e: # Connection is dead, close it and create a new one logger.warning(f"Existing connection is no longer valid: {str(e)}") try: _blender_connection.disconnect() except: pass _blender_connection = None # Create a new connection if needed if _blender_connection is None: _blender_connection = BlenderConnection(host="localhost", port=9876) if not _blender_connection.connect(): logger.error("Failed to connect to Blender") _blender_connection = None raise Exception("Could not connect to Blender. Make sure the Blender addon is running.") logger.info("Created new persistent connection to Blender") return _blender_connection