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Screenshot Tool — capture_screenshot

Captures the current screen and returns it as a JPEG image that Claude can see and describe.

@mcp.tool()
def capture_screenshot() -> Image:
    """Capture the current screen and return it as a JPEG image."""

This tool demonstrates returning binary data (not text) from an MCP tool using FastMCP's Image type. The image is compressed to JPEG at 60% quality to stay under Claude's ~1 MB attachment limit.

How It Works

buffer = io.BytesIO()
screenshot = pyautogui.screenshot()
screenshot.convert("RGB").save(buffer, format="JPEG", quality=60, optimize=True)
return Image(data=buffer.getvalue(), format="jpeg")
  1. pyautogui.screenshot() captures the full screen via the OS
  2. It's converted to RGB and saved as JPEG into a memory buffer
  3. FastMCP's Image wrapper sends it back to Claude as a base64-encoded image

Example Prompts

Take a screenshot of my screen and describe what you see

Capture my screen — is there anything unusual open?

Screenshot my screen and tell me what the main application is

Take a screenshot and summarize the content visible

macOS permissions

On macOS you may need to grant Screen Recording permission to your terminal app under
System Settings → Privacy & Security → Screen Recording.