note 110820 modified in function.json-decode by aharvey

First of all, since JSON is not native PHP format or even native JavaScript format, everyone who wants to use JSON wisely should carefuly read official documentation. There is a link to it here, in "Introduction" section. Many questions like "it doesn't recognize my strings" and those like previous one (about zip codes) will drop if you will be attentive! And second. I've found that there is no good, real working example of how to validate string if it is a JSON or not. There are two ways to make this: parse input string for yourself using regular expressions or anything else, use json_decode to do it for you. Parsing for yourself is like writing your own compiler, too difficult. Just testing result of json_decode is not enough because you should test it with NULL, but valid JSON could be like this 'null' and it will evaluate to NULL. So you should use another function - json_last_error. It will return error code of the last encode/decode operation. If no error occured it will be JSON_ERROR_NONE. So here is the function you should use for testing: <?php function isValidJson($strJson) { json_decode($strJson); return (json_last_error() === JSON_ERROR_NONE); } ?> It's so simple, that there is no need to use it and slow down your script with extra delay for function call. Just do it manualy in you code while working with input data: <?php //here is my initial string $sJson = $_POST['json']; //try to decode it $json = json_decode($sJson); if (json_last_error() === JSON_ERROR_NONE) { //do something with $json. It's ready to use } else { //yep, it's not JSON. Log error or alert someone or do nothing } ?> --was-- First of all, since JSON is not native PHP format or even native JavaScript format, everyone who wants to use JSON wisely should carefuly read official documentation. There is a link to it here, in "Introduction" section. Many questions like "it doesn't recognize my strings" and those like previous one (about zip codes) will drop if you will be attentive! And second. I've found that there is no good, real working example of how to validate string if it is a JSON or not. There are two ways to make this: parse input string for yourself using regular expressions or anything else, use json_decode to do it for you. Parsing for yourself is like writing your own compiler, too difficult. Just testing result of json_decode is not enough because you should test it with NULL, but valid JSON could be like this 'null' and it will evaluate to NULL. So you should use another function - json_last_error. It will return error code of the last encode/decode operation. If no error occured it will be JSON_ERROR_NONE. So here is the function you should use for testing: <?php function isValidJson($strJson) { json_decode($strJson); return (last_json_error() === JSON_ERROR_NONE); } ?> It's so simple, that there is no need to use it and slow down your script with extra delay for function call. Just do it manualy in you code while working with input data: <?php //here is my initial string $sJson = $_POST['json']; //try to decode it $json = json_decode($sJson); if (last_json_error() === JSON_ERROR_NONE) { //do something with $json. It's ready to use } else { //yep, it's not JSON. Log error or alert someone or do nothing } ?> http://php.net/manual/en/function.json-decode.php