[dilatedmind]

i would suggest bias your implementation against false negatives. They can always come back and update it if it's wrong, and their url could just as easily be "valid" but incorrect, eg any typo in a domain name.

if it's really important, you could try making a request to the url and see if it loads, but that still doesn't validate its the url they intended to input.

might be cool to load the url with puppeteer and capture a screenshot of the page. if they can't recognize their own website, it's on them.