I previously also made a domain name availability checking tool, but it only used DNS queries as first step. For more accurate results, it still needs to rely on WHOIS. https://query.domains

Cool but...it doesn't work, like pizza returns pizza.org and pizza.net as free.

I typed "test.io" in the input box and it checked for "test.io.org", "test.io.com" and even "test.io.io" but not "test.io".