import random


def init_config(num_particles, box_length):
    """
    Generates initial system configuration from a number of particles and box length.
    
    Parameters:
    ```````````
    num_particles : int
        The number of particles desired in configuration.
        
    box_length : float
        The length of the simulation box.
    
    Returns:
    ````````
    coordinates : list
        Nested list of coordinates [x,y,z] in configuration.
        
    box_length : float
        The length of the simulation box.
    
    """
    coordinates = []
    
    for i in range(num_particles):
        # generate random coordinates
        x = random.uniform(0, box_length)
        y = random.uniform(0, box_length)
        z = random.uniform(0, box_length)
        
        # add (x, y, z) to the list
        coordinates.append([x, y, z])
    
    return coordinates, box_length