After a few months of downtime (sorry!), the DNS tester is back.
It no longer uses the full list of nameservers from public-dns.tk, as it appears that someone is zmapping the entire IPv4 submitting every DNS server they find to the database (this was the cause of the downtime - my importer couldn't handle the large volume). Consequently the quality of data is now relatively poor and includes many dynamic addresses etc. For now I'm just using a subset of the servers (those that have been up reliably for at least several months), which should be good enough.
In the few days since launching my Global DNS Tester, I've made a few significant improvements. It's no longer limited to looking up A records alone; you can now compare A, AAAA, PTR, CNAME, NS, MX, and SOA records returned for any given host/IP from up to 100 public nameservers simultaneously.
I've also made a bunch of iterative improvements to the interface, and some minor performance improvements.
Helping a friend diagnose a DNS problem earlier, I stumbled across a huge list of public nameservers (more than 3,000 at present) at public-dns.tk. Inspired, I hacked together a simple script to query a random set of them and display the results.
So, I've just published a simple web based utility (URL at end of this post) for checking the A record of a hostname from a random set of global public nameservers. It allows you to query up to 100 servers at a time, either from all available global nameservers, or filtered by country. You might find it useful for diagnosing DNS propagation delays, nameserver connectivity issues, geotargeted DNS, and more. The nameserver list is updated about once an hour. I may release the source code at a later time, if I get around to cleaning it up a bit.