Tells you how long a certificate has left. One binary, no dependencies, no agent on the server.
$ sslwatch example.com portal.example.com:8443
example.com 67 days 2026-04-24 R11
portal.example.com:8443 12 days 2026-02-28 R11
go install github.com/NiklasKoehler/sslwatch@latest-q prints nothing while everything is fine, so cron only mails you when
something needs doing:
0 8 * * 1 sslwatch -q -days 21 example.com portal.example.com
Exit codes: 0 fine, 1 something is expiring, 2 something could not be checked.