MCP2Lambda

Instructions

Implementation Reference

• main.py:94-120 (handler)

  The core handler function for the 'invoke_lambda_function_impl' tool. Validates the function name, invokes the AWS Lambda function using boto3, handles errors, and formats the response payload.

  def invoke_lambda_function_impl(function_name: str, parameters: dict, ctx: Context) -> str:
      """Tool that invokes an AWS Lambda function with a JSON payload.
      Before using this tool, list the functions available to you."""
      
      if not validate_function_name(function_name):
          return f"Function {function_name} is not valid"
  
      ctx.info(f"Invoking {function_name} with parameters: {parameters}")
  
      response = lambda_client.invoke(
          FunctionName=function_name,
          InvocationType="RequestResponse",
          Payload=json.dumps(parameters),
      )
  
      ctx.info(f"Function {function_name} returned with status code: {response['StatusCode']}")
  
      if "FunctionError" in response:
          error_message = f"Function {function_name} returned with error: {response['FunctionError']}"
          ctx.error(error_message)
          return error_message
  
      payload = response["Payload"].read()
      
      # Format the response payload
      return format_lambda_response(function_name, payload)

• main.py:126-126 (registration)

  Registration of the invoke_lambda_function_impl tool using the mcp.tool() decorator in the generic tools strategy.

  mcp.tool()(invoke_lambda_function_impl)

• main.py:182-182 (registration)

  Fallback registration of the invoke_lambda_function_impl tool using the mcp.tool() decorator when dynamic registration fails.

  mcp.tool()(invoke_lambda_function_impl)

• main.py:35-38 (helper)

  Helper function used by the handler to validate Lambda function names based on prefix or explicit list.

  def validate_function_name(function_name: str) -> bool:
      """Validate that the function name is valid and can be called."""
      return function_name.startswith(FUNCTION_PREFIX) or function_name in FUNCTION_LIST

• main.py:56-65 (helper)

  Helper function used by the handler to format the Lambda response, preferring JSON pretty-printing.

  def format_lambda_response(function_name: str, payload: bytes) -> str:
      """Format the Lambda function response payload."""
      try:
          # Try to parse the payload as JSON
          payload_json = json.loads(payload)
          return f"Function {function_name} returned: {json.dumps(payload_json, indent=2)}"
      except (json.JSONDecodeError, UnicodeDecodeError):
          # Return raw payload if not JSON
          return f"Function {function_name} returned payload: {payload}"