Joern MCP Server

Instructions

@param class_full_name: The fully qualified name of the class
@return: List of full name, name, signature and id of methods in the class

Implementation Reference

• server_tools.py:67-75 (handler)

  The handler function implementing the 'get_class_methods_by_class_full_name' MCP tool. It is registered via the @joern_mcp.tool() decorator. The function sends a parameterized query to the Joern server using the joern_remote helper and parses the response into a list using extract_list.

  @joern_mcp.tool()
  def get_class_methods_by_class_full_name(class_full_name:str) -> list[str]:
      """Get the methods of a class by its fully qualified name
    
      @param class_full_name: The fully qualified name of the class
      @return: List of full name, name, signature and id of methods in the class
      """
      response = joern_remote(f'get_class_methods_by_class_full_name("{class_full_name}")')
      return extract_list(response)

• server.py:94-106 (registration)

  The generate() function in server.py dynamically executes server_tools.py, which defines and registers the tool via its @joern_mcp.tool() decorator during server startup.

  SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
  GENERATED_PY = os.path.join(SCRIPT_DIR, "server_tools.py")
  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:38-71 (helper)

  The joern_remote helper function, called by the tool handler to execute the actual Joern query on the remote server.

  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:38-45 (helper)

  The extract_list helper function parses the Joern query response into a structured list of method information (fullName, name, signature, id). Used by the tool handler.

  def extract_list(input_str):    
      """Extract a list of elements from a string representation of a Scala List.
      
      Parameters:
      input_str -- The input string containing a Scala List representation
      
      Returns:
      A Python list containing the extracted elements with cleaned data