I put together this handy little utility a few days ago to handle Domain to IP and IP to Domain lookup for an application we're working on. Results are returned as a plain text string, so no parsing will be required from any application that implements the resolver.
https://www.booksnbytes.net/misc/dns.php - Shows YOUR current public IP address (compare to whatismyip.com)
https://www.booksnbytes.net/misc/dns.php?ip=126.96.36.199 - Shows domain name associated with IP address 188.8.131.52 (if any)
https://www.booksnbytes.net/misc/dns.php?host=google.com - Shows the IP address associated with google.com. If the domain name is not registered, a convenient "available" message is returned instead.
Free to use for the time being, released closed-source under the MIT license. All usage is monitored, please don't abuse it without permission!