What is a thin vs thick registry or whois?

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’.

Domain Transfers

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
Whois Server: whois.example.com
Referral URL: http://domains.example.com
Status: clientTransferProhibited
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:

Domain ID:D892392839-LROR
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)
Registrant ID:reg-38444561
Registrant Name:Domain Owner
Registrant Organization:Domain Company Inc.
Registrant Street1:3551 15th Street
Registrant Street2:
Registrant Street3:
Registrant City:Sample City
Registrant State/Province: NY
Registrant Postal Code: 12345
Registrant Country: US
Registrant Phone:+1.2125551212
Registrant Phone Ext.:
Registrant FAX:+1.2125551212
Registrant FAX Ext.:
Registrant Email:[email protected]


Do not rely on the FTP Registry Transfer Report

Registrars that want to stay up to date on outgoing transfers and would like to give their registrars a timely chance to cancel stop pending transfer requests should not rely on the daily FTP reports provided by the Registry.

There are three methods available for obtaining information about the status of incoming & outgoing transfers:

  1. Transfer Reports from the registry FTP-Server
  2. EPP polling messages
  3. EPP Transfer Status Queries
  4. Transfer email messages

Most older registrar systems will rely solely on the FTP reports, which are not always published by the registry on times and have been delayed by several hours over the past years on several occasions. Considering that a transfer often takes five business days to complete, the user experience is already a bad one, so any additional delay should be avoided. Imagine an anxious registrant who is in the process of transferring their domain receiving an empty response from your whois server, since your system has not yet noticed that the transfer actually completed.

Experiences with most of the major registries have shown that it may not be a sound decision in a registrar implementation to rely on one only just one of the methods above. For .COM and .NET domains the Email Notifications are the most immediate and reliable method of receiving information about transfers. We recommend to poll these messages at least once an hour. Since email cannot be considered reliable today, we also recommend using the FTP report on top of the email notifications, which should be checked at least once daily. For full EPP registries, the polling notifications are the most direct information available.