validator.nu client-side

validator.js

// easy way to get current pages HTML
$.get('#', function(html) {

    // emulate form post
    var formData = new FormData();
    formData.append('out', 'json');
    formData.append('content', html);

    // make ajax call
    $.ajax({
        url: "http://html5.validator.nu/",
        data: formData,
        dataType: "json",
        type: "POST",
        processData: false,
        contentType: false,
        success: function(data) {
            console.log(data.messages); // data.messages is an array
        },
        error: function() {
           console.warn(arguments);
        }
    });
});