- json_decode: documentation ( source)
- str_replace: documentation ( source)
<?php
$str = '%u003c%u0062%u0072%u003e%u003c%u0064%u0069%u0076%u0020%u0063%u006c%u0061%u0073%u0073%u003d%u0022%u0074%u0065%u006c%u0065%u0066%u006f%u006e%u006f%u0073%u0022%u003e%u0036%u0035%u0031%u0033%u0034%u0037%u0036%u0035%u0030%u003c%u002f%u0064%u0069%u0076%u003e';
$str = str_replace('%u', '\\u', $str);
echo json_decode('"'.$str.'"');;
?>