Our APIs are documented in detail at this site:

http://domainindex.com/api

The description includes the details of the appraisal process and full technical specs of the API.
To use this API you need a registration at http://domainindex.com. The API key obtained along your registration should be used when testing the API. You can read about the subscriptions here.. Importantly, a free (but somewhat limited) subscription is also available after the registration.

The API key is valid for all APIs provided by domainindex.com.
In addition to the estimated price of a domain, this API provides additional information:

• Extracted keywords from the domain
• Local searches for domain
• Local per click (CPC) for the domain
• Local searches for the second-level domain
• Local CPC for the second-level domain
• Local searches for keyword
• Local CPC for keyword

(If the requested domain is gTLD then the location is All Countries. If the requested domain is ccTLD then location is the country of the TLD.)