You send a mail to an address - and then need to click "View Results". This sends you to "https://dkimvalidator.com/results" with a message of "I haven't received an email recently to....".
They do catch Ctrl-F5 keypress for reload. But if you just go to the URL bar and press enter you are returned to the front page with a new ID. You can paste the old address and then get the results but not a nice experience.
So. Nice domain name and points for effort. But a far cry away from https://www.learndmarc.com/ and the old dog https://www.mail-tester.com/ which both are really great. Less battery included but MxToolbox Supertool is still preferable to this (https://mxtoolbox.com/SuperTool.aspx).
Even shivdeepaks weekend project (https://dmarcverified.com) is more straight-forward and to the point.
So not to be a party pooper but as this was not a "Show HN" this is not really worth your time.