How to determine whether a string is valid JSON?

Question

Does anyone know of a robust (and bullet proof) is_JSON function snippet for PHP? I (obviously) have a situation where I need to know if a string is JSON or not.

Hmm, perhaps run it through a JSONLint request/response, but that seems a bit overkill.

Answer 1

If you are using the built in json_decode PHP function, json_last_error returns the last error (e.g. JSON_ERROR_SYNTAX when your string wasn't JSON).

Usually json_decode returns null anyway.

Answer 2

For my projects I use this function (please read the "Note" on the json_decode() docs).

Passing the same arguments you would pass to json_decode() you can detect specific application "errors" (e.g. depth errors)

With PHP >= 5.6

// PHP >= 5.6 function is_JSON(...$args) {     json_decode(...$args);     return (json_last_error()===JSON_ERROR_NONE); } 

With PHP >= 5.3

// PHP >= 5.3 function is_JSON() {     call_user_func_array('json_decode',func_get_args());     return (json_last_error()===JSON_ERROR_NONE); } 

Usage example:

$mystring = '{"param":"value"}'; if (is_JSON($mystring)) {     echo "Valid JSON string"; } else {     $error = json_last_error_msg();     echo "Not valid JSON string ($error)"; }