[Answer]-Django – custom error message for urlinput widget

The url type in Html5 will display required attribute message lilke this

Cross browser verbiage:
    Firefox: Please enter a URL.
    Chrome: Please enter a URL.
    IE: You must enter a valid URL

You can use setcustomvalidity

<form action="" method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Submit" />
</form>
<script type="text/javascript">
    document.addEventListener("DOMContentLoaded", function() {
    var elements = document.getElementsByTagName("INPUT");
    for (var i = 0; i < elements.length; i++) {
        elements[i].oninvalid = function(e) {
            e.target.setCustomValidity("");
            if (!e.target.validity.valid) {
                e.target.setCustomValidity("This field cannot be left blank");
            }
        };
        elements[i].oninput = function(e) {
            e.target.setCustomValidity("");
        };
    }
})
</script>