How to escape & in a POST request in jQuery?

Have you tried this syntax?

 data: {"id":id, "value": value, "type": type }

You can set your data option as an object and let jQuery do the encoding, like this:

$.ajax({
  type: "POST",
  url: "/admin/kategorie/add/link.json",
  data: { id: id, value: value, type: type },
  error: function(){ alert('Chyba! Reloadněte prosím stránku.'); }
});

You can encode each value using encodeURIComponent(), like this:

encodeURIComponent(value)

But the first option much simpler/shorter in most cases :)