serving UTFgrid information made with mb-util with leaflet

I've created the mbtiles file with tilemill and exported it on my ubuntu webfolder with the following command:

 mb-util --scheme=xyz /folder/tile.mbtiles /var/www/html/my-tiles

To get utfgrid information in my leaflet map itself I used danzels utfgrid plugin and the following code which is a nice copy of danzels example:

var tiles = L.tileLayer('http://localhost/my-tiles/{z}/{x}/{y}.png', {
            maxZoom: 9,
            attribution: '&copy; <a href="http://ift.tt/VGR6Z6">OpenStreetMap</a> contributors'
        });

        var utfGrid = new L.UtfGrid('http://localhost/my-tiles/{z}/{x}/{y}.grid.json');

        var map = L.map('map')
                .setView([50,10], 5)
                .addLayer(tiles)
                .addLayer(utfGrid);

A common error is written to the console:

ReferenceError: grid is not defined

So I've checke my grid.json files and they have the following coarse structure:

grid({"keys": ["", "6402"], "data": {"6402": {"namen": "cool name", "attrib 1": 0.123456}}, "grid": [" ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " !!! ", " !!!!! ", " !!!!!!! ", " !!!!!!!! ", " !!!!!!!!! ", " !!!! !!!! ", " !! !!!!! ", " !!! !!!!! ", " ! ! ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " "]});

Which looks fine for me. So what am i missing? In the example from milkator he is using:

        var utfGrid = new L.UtfGrid('http://ift.tt/1wGLbir}') 

Is there something to keep in mind using mb-util or anything else? My goal is to get the infromation from the UTF grid in a info box...