mitmproxy/libpathod/templates/response_previewform.html

<form class="form-inline" method="GET" action="/response_preview">
    <input id="spec" name="spec" class="input-medium search-query" value="{{spec}}">
    <input type="submit" class="btn" value="preview">
    <a href="#" id="submitspec" class="btn">go</a>
</form>
<script>
    $(function(){
        $("#submitspec").click(function(){
            document.location = "/p/" + $("#spec").val()
        });
    });
</script>