In a sharded environment there is no way to detect the originator of the query from either mongos or mongos. db.correntOp() reports all connections as originating from the mongos but there is no way to track it back to the originating client. Adding comments to the queries as suggested here http://docs.mongodb.org/manual/reference/operator/meta/comment/ is a workaround that does not help if queries are run manually (either authorised or non authorised users). Generally speaking having this info in Mongo itself seems to me like the right place.