// Retrieve a value:
$phpNative = Zend_Json::decode($encodedValue);

// Encode it to return to the client:
$json = Zend_Json::encode($phpNative);

Sometimes, it may be hard to explore JSON data generated by Zend_Json::encode(), since it has no spacing or indentation. In order to make it easier, Zend_Json allows you to pretty-print JSON data in the human-readable format with Zend_Json::prettyPrint().

// Encode it to return to the client:
$json = Zend_Json::encode($phpNative);
if($debug) {
    echo Zend_Json::prettyPrint($json, array("indent" => " "));
}

Second optional argument of Zend_Json::prettyPrint() is an option array. Option indent allows to set indentation string - by default it's a single tab character.