How to use the w3 validator API

Question

I currently have an online code editor and would like users to be able to validate their HTML code using the w3 validator on my site. When the user clicks check-code, this function is called:

$.get("//validator.w3.org/check", function(data) {
     alert(data);
});

But nothing happens. How do I incorporate the W3 validator in the AJAX request?

The documentation for the validator is here: http://validator.w3.org/docs/api.html