[{"_id":"https://www.example1.org/","invalid":3,"pending":6},{"_id":"https://example2.com/","invalid":10,"pending":4},{"_id":"https://www.example3.org/","invalid":2,"pending":6}]

db.collection.aggregate([{$group:{_id:null,pending:{$sum:"$pending"},invalid:{"$sum":"$invalid"},count:{$sum:1}}},{"$project":{_id:0}}])