How to use {% csrf_token %} in javascript

You are not sending the server generated csrf_token for the POST to verify the validity of the data. Hence the error.

As a part of the data part of the request, you need to send the token

csrfmiddlewaretoken: '{{ csrf_token }}' 

Something like this

var data = {
    url: item.find("#id_url").val(),
    title: item.find("#id_title").val(),
    tags: item.find("#id_tags").val(),
    csrfmiddlewaretoken: '{{ csrf_token }}' 
};

Or you could simply do:

var data = $('form').serialize()

if you want to send the whole form as a dictionary