Installing this code in your checkout template will enable SmartyStreets address validation for your billing and shipping addresses. It isn't currently working for multi-ship but it wouldn't be too hard to hack that support in.

You will need to create an account at https://smartystreets.com/account/create. They give away 250 free lookups per month but after that you have to pay for it. After creating your account, go to the API Keys page and create an HTML Key that's linked to your FoxyCart domain (yoursite.foxycart.com).

Paste the following code in your checkout template.

<script type="text/javascript">
function verify_address(address_type) {
 
	//Setup Vars
	var smarty_html_key = "ENTER YOUR KEY HERE";
 
	var address = $("#" + address_type + "_address1").val();
	var city = $("#" + address_type + "_city").val();
	var state = $("#" + address_type + "_state").val();
	var postal_code = $("#" + address_type + "_postal_code").val();
	var country = $("#" + address_type + "_country").val();
 
	//Not US, Skip
	if ($("#" + address_type + "_country").val() != "US") return;
 
	//Not Enough Vals, Skip
	if (!address || !city || !state) return;
 
	var url = "https://api.smartystreets.com/street-address?street=";
	url += encodeURIComponent(address);
	if ($("#" + address_type + "_address1").val()) url += encodeURIComponent(" " + $("#" + address_type + "_address2").val());
	url += "&city=" + encodeURIComponent(city);
	url += "&state=" + encodeURIComponent(state);
	url += "&zipcode=" + encodeURIComponent(postal_code);
	url += "&candidates=3&auth-token=" + smarty_html_key + "&callback=?";
	jQuery.getJSON(url, function(response) {
		$("#" + address_type + "_address_select").html("");
		if (response.length == 0) {
			$("#" + address_type + "_address_warning").show();
			return false;
		}
		if (response.length == 1) {
			var a = response[0];
			var address1 = a.delivery_line_1;
			var address2 = a.delivery_line_2;
			var city = a.components.city_name;
			var state = a.components.state_abbreviation;
			var postal_code = a.components.zipcode;
			if (a.components.plus4_code) postal_code += "-" + a.components.plus4_code;
 
			$("#" + address_type + "_address1").val(address1);
			$("#" + address_type + "_address2").val(address2);
			$("#" + address_type + "_city").val(city);
			$("#" + address_type + "_state").val(state);
			$("#" + address_type + "_postal_code").val(postal_code);
 
		} else if (response.length > 1) {
			var str = "<p>Your Address Had a Few Options:</p>";
			for (i = 0; i < response.length; i++) {
				var a = response[i];
				var address1 = a.delivery_line_1;
				var address2 = a.delivery_line_2 ? a.delivery_line_2 : '';
				var city = a.components.city_name;
				var state = a.components.state_abbreviation;
				var postal_code = a.components.zipcode;
				if (a.components.plus4_code) postal_code += "-" + a.components.plus4_code;
				str += '<p><a href="#" class="set_verified_address" data-address_type="' + address_type + '" data-address1="' + address1 + '" data-address2="' + address2 + '" data-city="' + city + '" data-state="' + state + '" data-postal_code="' + postal_code + '">';
				str += address1 + "<br>";
				if (address2) str += address1 + "<br>";
				str += a.last_line;
				str += "</a></p>";
			}
			$("#" + address_type + "_address_select").html(str).show();
 
		}
		$("#" + address_type + "_address_warning").hide();
		return true;
	});
}
 
jQuery(document).ready(function($){
	$("#customer_address1, #customer_address2, #customer_city, #customer_state, #customer_state, #customer_postal_code, #customer_country").change(function() {
		verify_address("customer");
	});
	$("#shipping_address1, #shipping_address2, #shipping_city, #shipping_state, #shipping_state, #shipping_postal_code, #shipping_country").change(function() {
		verify_address("shipping");
	});
	$(document).on("click", ".set_verified_address", function() {
		var address_type = $(this).attr("data-address_type");
		$("#" + address_type + "_address1").val($(this).attr("data-address1"));
		$("#" + address_type + "_address2").val($(this).attr("data-address2"));
		$("#" + address_type + "_city").val($(this).attr("data-city"));
		$("#" + address_type + "_state").val($(this).attr("data-state"));
		$("#" + address_type + "_postal_code").val($(this).attr("data-postal_code"));
		$("#" + address_type + "_address_select").html("").hide();
		return false;
	});
	$("#fc_customer_billing_list").append('<li id="customer_address_select" style="display: none;"></li><li id="customer_address_warning" style="display: none; color: #990000; font-weight: bold;">You may want to check this address as it appears it might have a problem.</li>');
	$("#fc_address_shipping_list").append('<li id="shipping_address_select" style="display: none;"></li><li id="shipping_address_warning" style="display: none; color: #990000; font-weight: bold;">You may want to check this address as it appears it might have a problem.</li>');
});
</script>

Developed by David Hollander http://foxytools.com/