Best debug tool to debug Ajax request in PHP

Best debug tool to debug Ajax request in PHP

What is the best debug tool to debug AJAX request in PHP? I want to check
whether the method in the class.php has been fired when the AJAX function
is calling.
Eg:
$.ajax({
url: 'classes/MyClass.php/GetItems',
data: {
'catgry': cat
},
dataType: 'json',
success: function (data) {
alert("data recived!");
},
error: function (jqxhr, textStatus, errorThrown) {
alert("error");
}
});
MyClass.php
public function GetItems($catgry) {
$ret = $itmObj->GetItemsByCat($catgry);
return $ret;
}