What documents are required for foreigners to visit India?

All U.S. citizens need a valid passport as well as a valid Indian visa or an Overseas Citizen of India (OCI) card, to enter and exit India for any purpose. ...
U.S. citizens seeking to enter India solely for tourist purposes for stays of less than 60 days may apply for an eVisa at least four days prior to their arrival.

Can I get visa on arrival in India?

In most cases, it shouldn't take more than 4 days for your Visa application to be approved but in some cases it can take up to 7 days. You won't be getting the New India Visa on Arrival at the airport as there is no paper equivalent for it but will have to apply for it online and pay for it online too.