CertFleet watches two things that take sites down and are usually monitored by two different products: TLS certificate expiry and HTTP uptime.
Staged alerts at 30/14/7/1 days, email/Slack/webhook, Certificate Transparency new-issuance alerts, DNS and domain-expiry monitoring, and public status pages.
Free forever for 10 certificates and 10 uptime monitors. The SSL checker needs no account at all.
