To get a really clean json string use these three constants like so:
<?php
$array = ['€', 'http://example.com/some/cool/page', '337'];
$bad = json_encode($array);
$good = json_encode($array, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES | JSON_NUMERIC_CHECK);
// $bad would be ["\u20ac","https:\/\/ptop.only.wip.la:443\/http\/example.com\/some\/cool\/page","337"]
// $good would be ["€","http://example.com/some/cool/page",337]
?>