list_modal_volumes

Retrieve a list of all Modal volumes with JSON output for managing cloud storage in serverless applications.

Instructions

List all Modal volumes using the Modal CLI with JSON output.

Returns:
    A dictionary containing the parsed JSON output of the Modal volumes list.

Input Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Implementation Reference

src/modal_mcp/server.py:95-111 (handler)

The main handler function for the 'list_modal_volumes' tool. It executes the Modal CLI command 'modal volume list --json', processes the JSON output using helper functions, and returns a standardized dictionary with volumes list or error details.

@mcp.tool()
async def list_modal_volumes() -> dict[str, Any]:
    """
    List all Modal volumes using the Modal CLI with JSON output.

    Returns:
        A dictionary containing the parsed JSON output of the Modal volumes list.
    """
    try:
        result = run_modal_command(["modal", "volume", "list", "--json"])
        response = handle_json_response(result, "Failed to list volumes")
        if response["success"]:
            return {"success": True, "volumes": response["data"]}
        return response
    except Exception as e:
        logger.error(f"Failed to list Modal volumes: {e}")
        raise

src/modal_mcp/server.py:15-40 (helper)

Core helper function used by list_modal_volumes to execute shell commands via subprocess, capturing stdout/stderr and handling errors.

def run_modal_command(command: list[str], uv_directory: str = None) -> dict[str, Any]:
    """Run a Modal CLI command and return the result"""
    try:
        # uv_directory is necessary for modal deploy, since deploying the app requires the app to use the uv venv
        command = (["uv", "run", f"--directory={uv_directory}"] if uv_directory else []) + command
        logger.info(f"Running command: {' '.join(command)}")
        result = subprocess.run(
            command,
            capture_output=True,
            text=True,
            check=True
        )
        return {
            "success": True,
            "stdout": result.stdout,
            "stderr": result.stderr,
            "command": ' '.join(command)
        }
    except subprocess.CalledProcessError as e:
        return {
            "success": False,
            "error": str(e),
            "stdout": e.stdout,
            "stderr": e.stderr,
            "command": ' '.join(command)
        }

src/modal_mcp/server.py:42-70 (helper)

Helper function called by list_modal_volumes to parse JSON from command stdout and standardize the response format with success/error handling.

def handle_json_response(result: Dict[str, Any], error_prefix: str) -> Dict[str, Any]:
    """
    Handle JSON parsing of command output and return a standardized response.
    
    Args:
        result: The result from run_modal_command
        error_prefix: Prefix to use in error messages
        
    Returns:
        A dictionary with standardized success/error format
    """
    if not result["success"]:
        response = {"success": False, "error": f"{error_prefix}: {result.get('error', 'Unknown error')}"}
        if result.get("stdout"):
            response["stdout"] = result["stdout"]
        if result.get("stderr"):
            response["stderr"] = result["stderr"]
        return response
    
    try:
        data = json.loads(result["stdout"])
        return {"success": True, "data": data}
    except json.JSONDecodeError as e:
        response = {"success": False, "error": f"Failed to parse JSON output: {str(e)}"}
        if result.get("stdout"):
            response["stdout"] = result["stdout"]
        if result.get("stderr"):
            response["stderr"] = result["stderr"]
        return response

src/modal_mcp/server.py:95-95 (registration)
The @mcp.tool() decorator registers the list_modal_volumes function as an MCP tool.
```
@mcp.tool()
```

Modal MCP Server