MCP-Slicer

Instructions

Implementation Reference

• src/mcp_slicer/mcp_server.py:187-305 (handler)

  The primary handler function for the 'capture_screenshot' tool, including the @mcp.tool() decorator for automatic registration in FastMCP. It handles input parameters to construct API requests to the 3D Slicer Web Server for capturing screenshots from application, slice, or 3D views. Processes the image response into base64 MCP ImageContent with accompanying text.
  @mcp.tool() def capture_screenshot( view_type: str = "application", view_name: str = None, slice_offset: float = None, slice_orientation: str = None, camera_axis: str = None, image_size: int = None ) -> list: """ Capture a screenshot from 3D Slicer's views. This tool provides real-time visual feedback of the current state of Slicer, enabling AI to observe the GUI and make informed decisions in a complete REACT loop. Parameters: view_type (str): Type of screenshot to capture. Options: - "application" (default): Full application window including all panels and views - "slice": A specific slice view (Red/Yellow/Green) - "3d": The 3D rendering view view_name (str): For slice views, specify which view to capture. Options: "red", "yellow", "green" Only used when view_type="slice" slice_offset (float): For slice views, offset in mm relative to slice origin. Only used when view_type="slice" slice_orientation (str): For slice views, specify orientation. Options: "axial", "sagittal", "coronal" Only used when view_type="slice" camera_axis (str): For 3D views, specify camera view direction. Options: "L" (Left), "R" (Right), "A" (Anterior), "P" (Posterior), "I" (Inferior), "S" (Superior) Only used when view_type="3d" image_size (int): Pixel size of output image (for slice and 3D views). Only used when view_type="slice" or view_type="3d" Returns: A list containing text and/or image content. The image is returned in MCP's standard format for proper display in AI clients. Examples: - Capture full application: {"tool": "capture_screenshot", "arguments": {"view_type": "application"}} - Capture Red slice view: {"tool": "capture_screenshot", "arguments": {"view_type": "slice", "view_name": "red"}} - Capture 3D view from anterior: {"tool": "capture_screenshot", "arguments": {"view_type": "3d", "camera_axis": "A"}} - Capture axial slice: {"tool": "capture_screenshot", "arguments": {"view_type": "slice", "view_name": "red", "slice_orientation": "axial"}} """ try: # Determine the API endpoint based on view_type if view_type == "application": api_url = f"{SLICER_WEB_SERVER_URL}/screenshot" params = {} description = "full application window" elif view_type == "slice": if not view_name: return [TextContent(type="text", text="Error: view_name is required for slice screenshots (red, yellow, or green)")] api_url = f"{SLICER_WEB_SERVER_URL}/slice" params = {"view": view_name.lower()} description = f"{view_name} slice view" # Add optional parameters if slice_offset is not None: params["offset"] = slice_offset if slice_orientation: params["orientation"] = slice_orientation.lower() description += f" ({slice_orientation})" if image_size: params["size"] = image_size elif view_type == "3d": api_url = f"{SLICER_WEB_SERVER_URL}/threeD" params = {} description = "3D view" # Add optional parameters if camera_axis: params["lookFromAxis"] = camera_axis.upper() description += f" from {camera_axis} axis" else: return [TextContent(type="text", text=f"Error: Invalid view_type '{view_type}'. Must be 'application', 'slice', or '3d'")] # Make the request to Slicer Web Server # Smart proxy handling: disable for localhost, use system default for others response = requests.get(api_url, params=params, proxies=get_proxy_config(api_url)) response.raise_for_status() # Check if response is an image if response.headers.get('Content-Type', '').startswith('image/'): # Convert image bytes to base64 image_base64 = base64.b64encode(response.content).decode('utf-8') # Return using MCP's content types return [ TextContent( type="text", text=f"Screenshot of {description} captured successfully" ), ImageContent( type="image", data=image_base64, mimeType="image/png" ) ] else: # Unexpected response type return [TextContent(type="text", text=f"Error: Unexpected response type: {response.headers.get('Content-Type')}")] except requests.exceptions.HTTPError as e: return [TextContent(type="text", text=f"HTTP Error {e.response.status_code}: {str(e)}")] except requests.exceptions.RequestException as e: return [TextContent(type="text", text=f"Connection error: {str(e)}. Make sure Slicer Web Server is running.")] except Exception as e: return [TextContent(type="text", text=f"Error: {str(e)}")]
• src/mcp_slicer/mcp_server.py:197-236 (schema)

  The docstring provides detailed schema information including parameter descriptions, types, options, usage examples, and return format for the capture_screenshot tool.
  Capture a screenshot from 3D Slicer's views. This tool provides real-time visual feedback of the current state of Slicer, enabling AI to observe the GUI and make informed decisions in a complete REACT loop. Parameters: view_type (str): Type of screenshot to capture. Options: - "application" (default): Full application window including all panels and views - "slice": A specific slice view (Red/Yellow/Green) - "3d": The 3D rendering view view_name (str): For slice views, specify which view to capture. Options: "red", "yellow", "green" Only used when view_type="slice" slice_offset (float): For slice views, offset in mm relative to slice origin. Only used when view_type="slice" slice_orientation (str): For slice views, specify orientation. Options: "axial", "sagittal", "coronal" Only used when view_type="slice" camera_axis (str): For 3D views, specify camera view direction. Options: "L" (Left), "R" (Right), "A" (Anterior), "P" (Posterior), "I" (Inferior), "S" (Superior) Only used when view_type="3d" image_size (int): Pixel size of output image (for slice and 3D views). Only used when view_type="slice" or view_type="3d" Returns: A list containing text and/or image content. The image is returned in MCP's standard format for proper display in AI clients. Examples: - Capture full application: {"tool": "capture_screenshot", "arguments": {"view_type": "application"}} - Capture Red slice view: {"tool": "capture_screenshot", "arguments": {"view_type": "slice", "view_name": "red"}} - Capture 3D view from anterior: {"tool": "capture_screenshot", "arguments": {"view_type": "3d", "camera_axis": "A"}} - Capture axial slice: {"tool": "capture_screenshot", "arguments": {"view_type": "slice", "view_name": "red", "slice_orientation": "axial"}} """
• src/mcp_slicer/mcp_server.py:187-187 (registration)

  The @mcp.tool() decorator registers the capture_screenshot function with the FastMCP server instance 'mcp'.
  @mcp.tool()