<?php // ADD $query='{ "errors":[] }'; $decode = json_decode($query, true); $data = ['uniq' => 'STR985']; foreach($data as $k => $v) { $decode['errors'][$k][] = $v; } // REMOVE $remKeys = ['uniq']; foreach($remKeys as $v) { if(array_key_exists($v, $decode['errors'])) { unset($decode['errors'][$v]); } } print_r($decode);