Got an email from Google today telling me that here was DNS Failure on one of my sites. So I checked the site - it's there. The thing is on the tools, they are looking for domain.com:/ - that's a colon and then a slash at the end. I have no idea what this means - is it a Google error, or is there sowing mystical going on that I don't know about? If I type that into a browsers, or clicks in the link in the email, I obviously get errors - either the site doesn't exist, or the URL name is invalid. The domain name is correct in Google's tools, so they must be adding this :/ either on purpose or it's an error on their part.

DNS is a mystery to me - so this may mean something, but in my experience, a DNS problem usually means the site can't be accessed. I leave it well alone.

Can I just check my understanding? if you use the correctly formed URL without the additional ":/" is the site reachable?

Yes. It's there as normal.

: & / aren't valid in DNS records/zones so it must be a google bug/error

Then don't worry as Saspro says its a google bug.

Thought it might be but wasn’t sure - thanks for confirming.