W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<body>

<?php
// An invalid json string
$string = "{'Peter':35,'Ben':37,'Joe':43}";

echo "Decoding: " . $string;
json_decode($string);
echo "<br>Error: ";

switch (json_last_error()) {
  case JSON_ERROR_NONE:
    echo "No errors";
    break;
  case JSON_ERROR_DEPTH:
    echo "Maximum stack depth exceeded";
    break;
  case JSON_ERROR_STATE_MISMATCH:
    echo "Invalid or malformed JSON";
    break;
  case JSON_ERROR_CTRL_CHAR:
    echo "Control character error";
    break;
  case JSON_ERROR_SYNTAX:
    echo "Syntax error";
    break;
  case JSON_ERROR_UTF8:
    echo "Malformed UTF-8 characters";
    break;
  default:
    echo "Unknown error";
    break;
}
?>

</body>
</html>