In my script I send data with cURL, and enabled CURLOPT_RETURNTRANSFER. The response is json encoded data. When I'm trying to json_decode, it returns null. Then I found that response contains utf-8 BOM symbols at the beginning of string (). There is some experiments: $data = $data = curl_exec($ch); echo $data; the result is {"field_1":"text_1","field_2":"text_2","field_3":"text_3"} $data = $data = curl_exec($ch); echo mb_detect_encoding($data); result - UTF-8 $data = $data = curl_exec($ch); echo mb_convert_encoding($data, 'UTF-8', mb_detect_encoding($data)); // identical to echo mb_convert_encoding($data, 'UTF-8', 'UTF-8'); result - {"field_1":"text_1","field_2":"text_2","field_3":"text_3"} The one thing that helps is removing first 3 symbols: if (substr($data, 0, 3) == pack('CCC', 239, 187, 191)) { $data = substr($data, 3); } But what if there will be another BOM? So the question is: How to detect right encoding of cURL response? OR how to detect what BOM has arrrived? Or maybe how to convert the response with BOM? Thanks.