Joern MCP Server

Instructions

Implementation Reference

• server_tools.py:98-106 (handler)

  The handler function for the get_method_full_name_by_id tool. It uses the @joern_mcp.tool() decorator for automatic registration and schema inference from type hints and docstring. The logic queries the Joern server remotely and extracts the result.
  @joern_mcp.tool() def get_method_full_name_by_id(method_id:str) -> str: """Retrieves the fully qualified name of a method by its ID @param id: The unique identifier of the method, the id is a Long int string, like '111669149702L' @return: The fully qualified name of the method (e.g., com.android.nfc.NfcService$6.onReceive:void(android.content.Context,android.content.Intent)) """ response = joern_remote(f'get_method_full_name_by_id("{method_id}")') return extract_value(response)
• server.py:32-32 (registration)

  Creation of the FastMCP server instance named 'joern_mcp' which is used to register all tools via decorators.
  joern_mcp = FastMCP("joern-mcp", log_level=log_level)
• server.py:96-106 (registration)

  Dynamic registration of tools from server_tools.py by executing its code, which applies the @joern_mcp.tool() decorators to register get_method_full_name_by_id and others.
  def generate(): """Generate and execute additional server tools from server_tools.py file. This function reads the content of server_tools.py and executes it to add more functionality to the server. """ with open(GENERATED_PY, "r") as f: code = f.read() exec(compile(code, GENERATED_PY, "exec")) generate()
• server.py:38-70 (helper)

  Helper function to send HTTP POST requests to the Joern server with the query and return cleaned stdout response, used by the tool handler.
  def joern_remote(query): """ Execute remote query and return results Parameters: query -- The query string to execute Returns: Returns the server response stdout content on success Returns None on failure, error message will be output to stderr """ data = {"query": query} headers = {'Content-Type': 'application/json'} try: response = requests.post( f'http://{server_endpoint}/query-sync', data=json.dumps(data), headers=headers, auth=basic_auth, timeout=timeout ) response.raise_for_status() result = response.json() return remove_ansi_escape_sequences(result.get('stdout', '')) except requests.exceptions.RequestException as e: sys.stderr.write(f"Request Error: {str(e)}\n") except json.JSONDecodeError: sys.stderr.write("Error: Invalid JSON response\n") return None
• common_tools.py:111-133 (helper)

  Helper utility to parse and extract the value from Joern query responses based on patterns, used in the tool handler to process the response.
  def extract_value(input_str: str) -> str: """Extract value from a string based on its pattern. This function automatically selects the appropriate extraction method based on the input string format: * If contains 'Long =', uses extract_long_value * If contains triple quotes, uses extract_code_between_triple_quotes * If contains single quotes, uses extract_quoted_string Args: input_str (str): Input string containing a value to extract Returns: str: Extracted value based on the detected pattern """ if 'Long =' in input_str: return extract_long_value(input_str) elif 'String = """' in input_str: return extract_code_between_triple_quotes(input_str) elif 'String = "' in input_str: return extract_quoted_string(input_str) else: return input_str