1. db.grep() -Search through all fields in all collections in a database for a value. By default it searches only indexed fields. To include non-indexed fields, specify the second parameter as true.

2. db.collection.fields() -list all keys in a collection -by default, it only checks 10100 documents to get an exhaustive list, if you document varies across the collection, do: db.collection.fields(true)

https://github.com/blowhacker/mongohelper