In a thin domain registry the domain contact information is held by the registrar. The registry whois just holds a referral to the registrar, the registration, expiry, update date, nameservers and domain status.
A thick domain registry holds all of the contact information needed for the domain names.
After a transition of .ORG to a thick whois in 2003 .COM and .NET are the only generic Top Level Domains (gTLDs) still using a thin registry. Many of the ccTLD (country code top level domain) registries that were running thin registries are switching to using the Extensible Provisioning Protocol (EPP) protocol for the registrars to communicate with them, which normally goes hand in hand with a ‘thick whois’.
In a thin registry, the contacts are not transferred as part of the transfer itself as the are in a thick registry. Thus the gaining/new registrar has to parse them when a domain is transferred or replace them with the contacts that were entered on the order. The lack of mandated registrar whois output format makes the parsing of whois information difficult.
Thin whois example:
Domain Name: EXAMPLE.COM
Registrar: EXAMPLE REGISTRAR LTD.
Whois Server: whois.example.com
Referral URL: http://domains.example.com
Name Server: NS1.NAMESERVER.COM
Name Server: NS2.NAMESERVER.COM
Updated Date: 15-mar-2013
Creation Date: 01-mar-2005
Expiration Date: 01-mar-2016
The remainder of the contact information would be provided by the sponsoring registrar.
Thick whois example:
Created On:23-Nov-2006 03:19:55 UTC
Last Updated On:19-Sep-2013 18:54:54 UTC
Expiration Date:23-Nov-2014 03:19:55 UTC
Sponsoring Registrar:Example Registrar Ltd. (R555-LROR)
Status:CLIENT TRANSFER PROHIBITED
Registrant Name:Domain Owner
Registrant Organization:Domain Company Inc.
Registrant Street1:3551 15th Street
Registrant City:Sample City
Registrant State/Province: NY
Registrant Postal Code: 12345
Registrant Country: US
Registrant Phone Ext.:
Registrant FAX Ext.:
Registrant Email:[email protected]