The following functions will check for and return valid JSON. Generally, json_last_error is best used to return the last error 
(if any) occurred during the last JSON encoding/decoding. The json_last_error function returns an integer but should be checked by way of the following constants:
The following will decode JSON and return either the resulting array or false (if the JSON returned an error).
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<?php
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function beliefmedia_check_json($json) {
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}
For debugging purposes, it's handy to know the precise error causing grief.
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<?php
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/*
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Check Valid JSON Data
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http://www.beliefmedia.com/code/php-snippets/check-valid-json
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*/
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function beliefmedia_json_validate($string) {
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/* Check is_string and not empty */
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/* Decode the JSON data */
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/* Switch and check for possible JSON errors */
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case JSON_ERROR_NONE:
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$error = ''; // JSON is valid // No error has occurred
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break;
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case JSON_ERROR_DEPTH:
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$error = 'The maximum stack depth has been exceeded.';
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break;
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case JSON_ERROR_STATE_MISMATCH:
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$error = 'Invalid or malformed JSON.';
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break;
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case JSON_ERROR_CTRL_CHAR:
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$error = 'Control character error, possibly incorrectly encoded.';
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break;
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case JSON_ERROR_SYNTAX:
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$error = 'Syntax error, malformed JSON.';
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break;
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// PHP >= 5.3.3
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case JSON_ERROR_UTF8:
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$error = 'Malformed UTF-8 characters, possibly incorrectly encoded.';
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break;
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// PHP >= 5.5.0
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case JSON_ERROR_RECURSION:
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$error = 'One or more recursive references in the value to be encoded.';
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break;
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// PHP >= 5.5.0
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case JSON_ERROR_INF_OR_NAN:
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$error = 'One or more NAN or INF values in the value to be encoded.';
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break;
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case JSON_ERROR_UNSUPPORTED_TYPE:
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$error = 'A value of a type that cannot be encoded was given.';
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break;
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default:
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$error = 'Unknown JSON error occured.';
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break;
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}
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if ($error !== '') {
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// Throw the Exception or exit
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exit($error);
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}
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/* JSON OK */
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return $result;
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}
Source: Stackoverflow/Madan Sapkota.
