How precisely can a domain name's availibility be based upon checking for the presence of NS or SOA (Oncoming of Authority) records?

Otherwise, how can one know for sure as precisely as you possibly can without turning to WHOIS? For instance, could it be worth checking for MX records if no NS records exist?

I'm particularly thinking about domain names, however the only official, fool-proof method to check availability within the namespace is by using, which limits consecutive checking by Ip.

The only real 100% reliable method to look for domain availability would be to query the registrar's database. I wouldn't trust whois.

You should use DNS to obtain an estimate. Rather than searching for an SOA record, I'd just turn to see contrary whatsoever shows up using the TLD title server. search is a great tool with this (operates on Home windows, too), although I suppose you could utilize nslookup too. For instance:

search NS

will give you a listing from the title servers for Among individuals servers is

Next, query that server directly to ascertain if they've anything listed for the domain of great interest:


That question returns NS records, but no SOA record since SOA records are supplied through the domain's title server (which might be online). The NS records indicate the domain title is being used.

The reason behind going direct is the fact that it's often considerably faster than depending on recursive queries out of your local title server.

Whois may be the canonical method to look for domain availability. The speed restricting can there be deliberately to help keep folks from over-loading the whois servers. Information on SOA records might be a good guess, however it is not a particular answer.

Used, the DNS research works 99% of times. Should you writing something similar to Ajaxwhois, I'd suggest going this route. For those who have millions of names to check on, I'd perform a first pass having a DNS research, after which maybe perform a second spread those which you might consider buying.

  • Whois may be the only 100% sure method of checking for domain availability. See
  • My tests reveal that checking for the presence of NS records or ANY DNS records in large quantities appears to become probably the most accurate method of speculating whether b domain can be obtained for registration. SOA records work too, although not too.
  • search NS shows TLD nameservers. Ping TLD servers and employ the nearest ones to prevent unncessary recursive queries.

Interesting solutions.

I have been while using search approach to test for the presence of a website before signing up but about 10% of times, it returns domain names that aren't available as available. The reason being who owns the domain has not setup any records for that domain. What exactly I have made the decision to complete is:

  1. First check via search method.
  2. If domain seems to be shown, then check using whois.shtml

Individuals will undergo a lot of domain names that aren't available which does not waste the allotted demands that UniForum provides. Only when something seems to be shown would you check up on itself. It appears in my experience to be the sole reliable method of doing this WITHOUT losing use of because of delivering them millions of demands :)