The tool https://crt.sh/ is a certificate log monitor. So it’s visible how many certificates are created with a domain name.
But: There are some problems:
Log monitor stopped, and Upcoming Changes
crt.sh startet 2015-06, before Letsencrypt.
The idea that “2 billion certificates ought to be enough for any PKI” (to misquote Bill Gates) didn’t seem that daft to me back when crt.sh was born (June 2015). Let’s Encrypt had not yet launched, there were only a few million active certificates in the WebPKI (https://blog.cloudflare.com/introducing-universal-ssl/), and certificate lifetimes of >=1yr were the norm. However…
Yesterday, there was an int32-overflow.
Now a new database is startet.
The new database is currently busy importing data and building indexes. I’m hoping it’ll be production-ready and available by early next week (caveat: I am rubbish at predicting ETAs). I’ll update this thread with more details when I have them.
Perhaps next week … the tool may work again.