Onionscanner
This was one of the first scripts I worked on, back in 2016. At that times, links for Onion Services V2 still had 16 characters, against the 52 of today's V3.
Onionscanner is a simple multithreaded python scanner, which tries to bruteforce valid onion domains or check a user-provided list of onion urls.
It requires a socks4 tor proxy listening on 127.0.0.1:9050.