Checking if an Index exists in mongodb

Creating indexes in MongoDB is an idempotent operation. So running db.names.createIndex({name:1}) would create the index only if it didn’t already exist.

The deprecated (as of MongoDB 3.0) alias for createIndex() is ensureIndex() which is a bit clearer on what createIndex() actually does.

Edit:
Thanks to ZitRo for clarifying in comments that calling createIndex() with the same name but different options than an existing index will throw an error MongoError: Index with name: **indexName** already exists with different options as explained in this question.

If you have other reasons for checking, then you can access current index data one of two ways:

1. As of v3.0, we can use db.names.getIndexes() where names is the name of the collection. Docs here.
2. Before v3.0, you can access the system.indexes collection and do a find as bri describes below.